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Even business PC stalwarts like Dell and Gateway now sell exotic gaming machines with CPUs that they've overclocked for you. In our tests of Dell's new XPS 720 gaming desktop, benchmarked with and without Dell's factory tweaks, we found that the system's overclocking boosted its performance by 6.5 percent.

Each of the desktops ranked in our chart--which also includes new PCs from Alienware and Gateway--boasts an overclocked CPU. The key benefit of buying such a machine: Left at its stock settings, the revved-up chip is covered under the system's warranty--a safety net you don't enjoy when you overclock the CPU in a gaming rig you've built yourself. Our Best Buy, CyberPower's Gamer Infinity Ultimate, is equipped with a quad-core 2.66-GHz Core 2 Extreme QX6700 processor (set to 3.46 GHz). The system earned a score of 129 in WorldBench 6 Beta 2, the highest result achieved by any PC we've tested to date. The Gamer Infinity Ultimate may lack the customized touches you'll see from boutique vendors such as Alienware and Voodoo, but it packs a lot of value for gamers and power users who need speed, storage, and the ability to upgrade.

Polywell Computers' Poly 580CF-2900 (the least expensive system we tested at $3399, and one that doesn't come with an overclocked CPU) missed the chart because of its WorldBench 6 Beta 2 score of 93, a result roughly 26 percent behind its rivals' average of 126.