Average performance
If you can't be bothered to study all of our charts and scatter plots... well, you probably should anyway. Our synthetic average-performance-versus-price plot is seducingly straightforward, but it's very much an artifact of our test suite, which probably consists of more multi-threaded apps than what your typical enthusiast might run.

To create a synthetic "performance" score, we computed an unweighed average for results in all 22 of our benchmarks (including the WorldBench overall score). As our baseline, the Athlon X2 6400+ gets a 100% score. Other scores are all relative to it.

Since our aggregate performance scores are somewhat biased toward multithreaded tests, the Core 2 Quad Q8200 looks like a better overall deal than the Phenom II X3 720—even though the X3 720 leads in non-multithreaded tasks.

Looking at the rest of the plot, we can spot several other trends. The Core 2 Quad Q9400 and Phenom II X4 940 are neck-and-neck, but the X4 920 outperforms the Q9300. That means the 920 may be a better overall deal than the Core 2 Quad Q8300, which has the same clock speed but less cache than the Q9300. (The 920 and Q8300 are both priced almost identically, although the AMD offering is slightly cheaper at Newegg.) In plainer terms, AMD's high-end quad-core offerings are refreshingly competitive.

Looking further north, the Core i7-920 distances itself from the pack quite a bit overall. This is probably a good time to start looking at how full system pricing factors into the Core i7 formula, though. Let's do that now.

Below, you'll see another scatter plot with the same aggregate performance scale on the Y axis. To get our pricing numbers for the X axis, we've added the cost of a motherboard, memory kit, graphics card, and hard drive to that of our processors. Wherever it made sense, we picked components from our latest system guide. Also, we got all our prices from Newegg. Here's a complete breakdown:

So, does the value picture change at all when we do this?

The Core i7-920 does look less appealing when we factor in the cost of other parts, but it still seems like a worthwhile step up. Looking at the lower portion of the graph, it's also clear that cheaping out on a processor doesn't impact the cost of a full system as much as one might think. At least, going from our baseline Athlon to a Phenom II X4 940 only raises the full system price from $506 to $641. That's a 27% price increase (less once you throw in an enclosure, monitor, and all that jazz), but at least here, you get a 56% overall performance increase in return.

Speaking of the Phenom II X4 940, we didn't just pick it as a random example—this processor really looks particularly compelling. It's a somewhat better deal than the Core 2 Quad Q9550, and it's not only as fast as the Q9400, but also slightly cheaper when we account for the lower prices of AMD enthusiast motherboards. (Actually, the X4 940 is 30 bucks cheaper than the Q9400 on Newegg right now, even though official price lists give the advantage to the Q9400.) You might find the X4 920 more enticing because of its even lower price, but the 940 has an unlocked upper multiplier, which can make overclocking considerably easier.