The chaps over at Neoseeker have published a look at Core 2 Duo Scaling in some recent games. Here's an excerpt:

To sum up the results of the benchmarks, the speed of our E6700 had almost no affect on the Call of Juarez -- the GPU was the only bottleneck to performance in that case. For Crysis on medium graphic settings, the CPU had a significant impact on framerates, but after about 2.2 GHz, the impact was less severe. Also for Unreal Tournament 3, and World In Conflct, 2.2 GHz seemed to be the 'magic speed.' The difference between 2.2 GHz and 3.0 GHz was not that great for any of the four games tested.

Another important conclusion you can draw from this article is that at resolutions above 1280x1024, it looks like you almost most certainly will be bottlenecked by your GPU, and not your CPU. If you have an older monitor and game at 1280x1024, it might be worth it to overclock your computer if you have a processer slower than a Core 2 Duo at 2.2 GHz. On the otherside of the coin, if you have a game at higher resolutions -- like 1680x1050 for instance -- you'll benefit less from any CPU overclocking you could do, so it may be better for you just to be kinder to CPU and prolong its lifespan.

If you are about to buy yourself a new gaming rig, then it probably is best to cut from the CPU budget, and put more into your GPU budget. It looks like it'll be some time (perhaps a very, very long time) before most games become more demanding on the CPU than the GPU. And it'll be an even longer time before any game comes out that really makes full use of the parallel processing power of a quad core system. For the overclockers out there, a E2160 or E2180 can be had for less than $100, and can propel you well above the 'magic' 2.2 GHz performance plateau. For example, or E2160 we tested in the lab ran at 3.2 GHz stable, on air-cooling alone. While it is true that CPU prices are falling fast -- the newly released 3GHz E8400 Wolfdale Core 2 Duo just became available purchase this week, for only $220 USD -- if you are on a tight budget, you still might want to tighten up your CPU belt in order to loosen up your GPU belt.