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The value proposition
Now that we've buried you under mounds of information, what can we make of it all? One way to filter the information is to consider the value proposition for each CPU model. Exercises like this one are inherently fraught with various, scary dangers—giving the wrong impression, committing bad math, overemphasizing price, coming off as irredeemably cheesy—but our value comparisons have proven to be popular over time, so we've taken another crack at it.

What we've done is mash up all of our performance data in one, big summary value for each processor. The performance data for each benchmark was converted to a percentage using the Pentium 4 670 as the baseline. We've included nearly every benchmark we used in our overall index, with the exception of the purely synthetic tests like Stream. We excluded MyriMatch, Euler3D, and Folding@Home, since not all processors were tested in those benchmarks. In cases where the benchmarks had multiple components, we used an overall mean rather than including every component score individually. Each benchmark should thus be represented and weighted equally in the final tally. (The one case where we didn't average together a single application's output was WorldBench's two 3ds max tests, since one measures 3D modeling performance and the other rendering.)

This overall performance index makes us a little bit wary, because it's simply a mash-up of results from various tests, rather than an index carefully weighted to express a certain set of priorities. Still, our test suite itself is intended to cover the general desktop PC's usage model, so the index ought to suffice for this exercise.

We then took prices for each CPU from the official Intel and AMD price lists. For our historical comparison, we've also included the Core 2 Quad Q6600 and the Pentium 4 670 in a couple of places at their initial launch prices.

If we simply take overall performance and divide by price, we get results that look like this:

By this measure, you should almost always buy one of the cheapest CPUs on the market. This bar chart gives us a strong sense of value, but it may focus our attention a little too exclusively on CPU prices alone. For many of us, time is money, and faster computer hardware is relatively inexpensive. What we really want to know is where we can find the best combination of price and performance for our needs. To give us a better visual sense of that, we've devised our nefarious scatter plots.

The faster a processor is, the higher on the chart it will be. The cheaper it is, the closer to the left edge. The better values, then, tend to be closer to the top-left corner of the plot. If you wish, you can find your price range and look for the best performer in that area.

AMD's new Phenom II X6 processors fare rather well here. The X6 1055T eclipses its closest rival, the Core i5-750. Meanwhile, the 1090T falls between the Core i7-930 and the much pricier Core i7-870 on both the performance and price axes.

That gets us closer to the heart of the matter, but in reality, the price of a processor is just one component of a PC's total cost, and the various platforms do have some price disparities between them. Echoing our last CPU roundup, we fashioned some sample systems loosely based on the Utility Player build in our latest system guide for each platform type. Our goal was to achieve rough parity by selecting full-sized ATX motherboards with similar, enthusiast-friendly feature sets. Here are the components we picked for the different platforms, along with system prices:

Platform Total price Motherboard Memory Common components
AMD 890GX $656.94 Asus M4A89GTD Pro
($139.99)
4GB Kingston DDR3-1333
($104.99)
XFX Radeon HD 5770 1GB graphics card ($159.99), Western Digital Caviar Black 1TB hard drive ($109.99), Samsung SH-S223L DVD burner ($26.99), Antec Sonata III case with 500W PSU ($114.99)
Intel P45 $656.94 Gigabyte GA-EP45T-USB3P
($139.99)
Intel P55 $649.94 Gigabyte GA-P55-UD3
($132.99)
Intel X58 $789.94 Gigabyte GA-X58A-UD3R
($199.99)
6GB OCZ DDR3-1600
($177.99)

What happens when we factor these rather considerable system prices into our value equation?

Whoa. Not just one, but both of the Phenom II X6s dethrone the Core i5-750. We can probably attribute these rankings to the six-core AMD chips' much higher performance in highly multithreaded tasks, since the Phenom II X6 1055T often falls close to (and sometimes below) the i5-750 in other apps.

The scatter plot gives us a little more context and highlights another interesting matchup: that of the Phenom II X6 1090T versus the Core i7-930. While both processors perform roughly in the same ballpark in our test suite overall, the Intel chip requires relatively expensive X58 motherboards and triple-channel memory kits, while the AMD chip works happily in more affordable 890GX mobos (and even cheaper Socket AM3 offerings) with dual-channel RAM. The 1090T ends up looking somewhat more attractive as a result.

Performance per dollar isn't the whole story these days, though. The power efficiency of a processor increasingly helps determine its value proposition for a host of reasons, from total system costs to noise levels to the size of your electric bill. We measured full system power draw and considered efficiency earlier in this article; now, we can factor in system prices to give us a sense of power-efficient performance per dollar.

Despite making inroads on the performance-per-dollar front, AMD still hasn't quite nabbed the power-efficiency value crown, which falls upon the Core i5-750 once again. The Phenom II X6 1090T still manages to outdo the Core i7-870, though.