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Overall performance
For those who have diligently sifted through each page of scatter plots and hopefully not-too-tedious analysis, congratulations. Seriously, you deserve a medal or something. Those who skipped ahead to this page will receive no such praise. They will, however, get a nice summary of performance with a single overall score.

Using a single number to represent a drive's performance across a range of different benchmark tests can be tricky business. After reading through numerous papers on the subject, we've settled on calculating a harmonic mean of all the results you've seen today. A harmonic mean can be useful for quantifying overall performance for a benchmark suite when individual test results can be compared to a reference baseline, and it's not prone to being skewed by the fact that we have performance differences of several orders of magnitude in some cases. We just happen to have a full suite of results normalized to our ancient Travelstar baseline, and as you'll see in a moment, the harmonic mean generates an overall score that nicely tracks with the value propositions we've observed thus far.

I should note that we originally intended to use an arithmetic average to calculate our overall score. However, this simple mean was skewed by some of the enormous performance gaps in IOMeter and HD Tune's random access time tests, which are several orders of magnitude larger than the performance deltas in the other tests. The resulting overall score didn't track with expectations based on the value we've already quantified in individual tests. Weighting the average to account for those orders-of-magnitude differences would have been arbitrary at best, so we've settled on a harmonic mean, which seems to provide useful results.

Our overall score includes individual results for DriveBench and IOMeter rather than the averages we presented in the first set of value graphs. There are five DriveBench multitasking loads and four IOMeter access patterns, giving us a total of 19 test results from which to calculate the harmonic mean. This collection of tests is a little biased towards random access patterns rather than sequential transfers, but we think that makes perfect sense for those contemplating an SSD for an OS and applications drive. The power-efficiency results have been left out to keep this a strictly performance-per-dollar affair.

Because they had to sit out at least one of the tests that make up our overall average, the PX-128M1S and X25-V RAID array haven't been included in the graphs below. We wouldn't recommend the former, anyway, and with two drives at its disposal, the RAID config would've had an unfair advantage—you know, like it's had all day already.

The RealSSD easily offers the highest overall performance of the lot. Corsair's Nova V128 sneaks into second place ahead of a trio of SandForce-based offerings, followed by the X25-M and the Force F120. How do things shake out when this overall score is combined with our value calculations?

Quite well, at least for the RealSSD. On a cost-per-gigabyte basis, the Crucial drive clearly offers better value than any of the other SSDs. It's one of the least expensive drives on that scale, and its overall performance is unmatched by even the priciest options.

The X25-M looks pretty good here, as well. It's not as fast as the RealSSD, but you'll pay a little bit less per gigabyte. The Nova is also an interesting option, offering better performance for a little extra scratch.

Paying more per gigabyte for the SandForce drives doesn't make a whole lot of sense in this context. They lie between the Nova and X25-M on the performance scale but cost more per gigabyte than both. Even the F120 has a higher cost-per-gigabyte than the Nova and X25-M, and it's slower than both of them.

Despite strong showings in quite a few tests, the SSDNow doesn't look all that attractive overall. Neither does the X25-V or the SiliconEdge Blue.

Next, we'll mix things up with a look at performance per dollar in the context of total system cost. The aim here is to determine whether spending a little (or a lot) more on an SSD makes sense when the price premium is absorbed as part of the cost of a complete system. The step up from a $300 drive to a $400 one is daunting if that's all you're buying, but it's relatively less imposing if you're simply nudging a $1300 build up to $1400.

Unfortunately, the higher-capacity drives will unavoidably be at a disadvantage with these calculations due to their higher prices. With a street price dangerously close to $100, the X25-V won't be adding much to the bill for our complete system, giving the Intel drive a distinct edge over the competition. Just remember that with only 40GB, the X25-V isn't adding much to the system's storage capacity, either.

For our system price calculations, we've used our test rig as the inspiration for a base config, to which the price of each drive will be added. Our example system includes a Core i5-750, a P55-based ASUS P755D-E motherboard, 4GB of DDR3-1333 memory, a Caviar Black 1TB drive for mass storage, a passively-cooled Radeon HD 4850, Antec's Sonata III enclosure, and Windows 7. Its base price is $939.93.

Here's the big payoff, folks. In the context of a larger system purchase, one can indeed justify stepping up to an SSD. In fact, the SSDs dominate this metric, which admittedly focuses on storage performance rather than overall system speed. The numbers speak for themselves, though: going with an SSD can make sense if you're already plunking down a sizeable chunk of change on a system.

Having said that, one should note that using the total system price in our value calculations penalizes the RealSSD and the SiliconEdge because they more expensive drives due to their higher capacities. The SiliconEdge's mediocre overall performance is much more of a hindrance, though. At least the C300 has chart-topping performance to fall back on.

The sweetest spot on this particular scale appears to be occupied by the Nova V128. This Indilinx-based drive has the second-best overall performance and a lower price than the X25-M. The Agility and Vertex are cheaper still, although they're both a little bit slower overall.

One should keep differences in capacity in mind when comparing the X25-M to the Agility, Vertex, and Force F100. The SandForce drives score a little higher on our overall performance scale, and the OCZ models cost less than the Intel drive. However, the X25-M packs 160GB, while that lead group of SandForce offerings only serves up 100GB of storage capacity each.

In one more nefarious twist, we can attempt to correct for the capacity differences by factoring in cost per gigabyte, as we've done all along. By doing so in the context of system prices, we get a complicated metric—performance per dollar per gigabyte using the total system cost—that gives us a rather different indicator of the value propositions offered by these SSDs.

Nothing has changed on the performance scale, but the scatter plot looks very different thanks to movement along the X axis. The RealSSD is very close to the ideal upper-left corner, offering easily the best performance at a lower price per gigabyte than any other SSD. None of the other SSDs even come close.

Behind the C300, the X25-M and Nova can both make a case for second best. The Nova is the faster of the two, while the Intel drive is the cheaper option. Both are preferable to the SandForce SSDs, which sit between the Nova and the X25-M on the performance scale but cost quite a bit more than both of them.

Way off to the right is the X25-V, whose paltry 40GB capacity does the drive no favors. The higher-capacity SSDs do have an advantage with this particular value calculation because we're dividing the total system cost by the capacity of each drive.