In Doom 3, we found that there was absolutely no CPU limitation at all, and there was no difference in the quality of game play between a CPU from the 3000+ to 3200+ region, and the top-of-the-line Athlon 64 FX-55. With the CPU clocks reduced some 800MHz, we were still able to enjoy a smooth gaming experience at 1600x1200 4xAA 8xAF at High Quality. We experienced a slight three frames per second drop in minimum frame rate, but it was still in the high 20's meaning that game play was more than acceptable.
We suspect that titles based around the Doom 3 engine, such as Quake 4, will also benefit from good, solid SLI performance with a slower processor. Before you jump to any conclusions that all titles offer the same versatility as Doom 3 does in the CPU department, lets have a look across our chosen selection of titles.
In complete contrast, Half-Life 2 shows the other end of the spectrum. We were able to maintain the quality settings used on the Athlon 64 FX-55 on our pseudo 3700+, with no drop in minimum frame rate. However, there was a massive drop in our average frame rate, which meant that the game play was not quite as smooth as we experienced on the Athlon 64 FX-55.
When we throttled the FX-55 further, to represent an Athlon 64 with a PR value of around 3000+ to 3200+, we found that we also had to lower our detail settings slightly to improve the game play quality. At 1600x1200 4xAA 16xAF 'Reflect All' on our pseudo 3100+, we had problems with choppiness in parts of our manual run through, and thus we had to reduce the Anti-Aliasing quality from 4x to 2x.
We also experienced further drops in the average frame rate, making the game-play experience a little less enjoyable. It proves that the title has a large number of very CPU limited levels.