Conclusion
Now, I’ll try to sum everything up. First of all, the single Radeon HD 5870 does not depend as much on the CPU as it is supposed to. According to my tests (the left part of the diagrams),
the Radeon HD 5870 is quite satisfied with an overclocked dual-core CPU manufactured two years ago. And you can even leave the CPU at its default frequency at the high-quality settings and 1920x1200. The only exceptions are
Left 4 Dead and
Warhammer 40000: Dawn of War II. The former game is not a problem for modern top-end Radeons while the latter, on the contrary, calls for a quad-core CPU, preferably from Intel.