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The new value mix
Since the 875K and 655K don't break any new ground in terms of stock clock frequencies, we'll spare you the massive CPU benchmark comparison. You can look at our Phenom II X6 review if that's what you want. We're instead going to focus on overclocking the K series.

Before we go there, though, we should take a quick look at how the effective price cut heralded by the 875K's release changes the value picture. To get a sense of that, we've taken the performance and value data from our Phenom II X6 review and modified the prices slightly. Since we're only considering stock clock speeds here, we've used performance data from the Core i7-870 to represent the 875K—the two should perform identically. Only a handful of the CPU prices have changed since that comparison, mostly for lower-end Athlon II processors.

A simple look at the price-performance ratio gets us this:

The cheaper processor almost always comes out on top if you run the numbers like this. As you can see, the 875K doesn't fare so well on this basis. We don't think that's entirely fair, though, which is why we came up with our scatter plots that show both price and performance at the same time.

That looks much more promising. In fact, the 875K is in a very nice spot. To get higher performance than it, you'll pay substantially more money.

Then again, CPU purchase decisions are usually made as part of a complete system build, and the math changes quite a bit when we consider price and performance in that context. In our X6 review, we priced out a comparable set of system components for each platform we tested, and it wound up looking like so:

Platform Total price Motherboard Memory Common components
AMD 890GX $656.94 Asus M4A89GTD Pro
4GB Kingston DDR3-1333
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
Intel P55 $649.94 Gigabyte GA-P55-UD3
Intel X58 $789.94 Gigabyte GA-X58A-UD3R
6GB OCZ DDR3-1600

If you consider performance per dollar in the context of a mid-range system build like this one, the results change dramatically.

The 875K is our new value leader, just ahead of the Phenom II X6 1090T Black Edition. There's very little daylight between the 875K and the 1090T, but the 875K comes out ahead.

The scatter plot illustrates the dynamic: the 875K's additional performance offsets its higher price. Of course, none of this analysis takes overclocking into account, so it is just a starting point. Not a bad starting point, though!

We have a new leader in power efficiency per dollar, as well—by a very tiny margin over the old champ, the Core i5-750. The X6 1090T just isn't as power-efficienct as Intel's best chips.