I'm talking about CPU bottlenecking the GPU in gaming - not if getting a better cpu will improve game performance. I never said overclocking is pointless for gaming. Getting a better CPU will improve his gaming experience...as will overclocking. But the improvement will not be significant if you already have a Core2.
His Q9400 CPU will NOT bottleneck a GTX260. And a 2.0GHz Core2 is also highly unlikely to bottleneck a GTX260.
Why? Because games are still overwhelming GPU dependent, NOT CPU dependent. Games only become primarily CPU dependent when:
1. The game requires a lot of CPU power for the GPU or the game itself (ie. SLi systems)
2. you've already maxed out your GPU requirements for the game (ie. tri Sli GTX280s on Crysis ultra high)
3. Playing a hardware intense game on low graphics/resolutions
CPU bottlenecks are extremely rare compared to GPU bottlenecks, which will be his problem when playing Crysis. As for all the other games you've mentioned, a 2.0 GHz Core2Duo paired with a good graphics card will get enough frames per second that the human eye can't tell the difference.
Gamespot examination of CPU bottlenecking in Crysis.
"The CPU becomes less of a bottleneck when we bump up the graphical complexity. If you have a single-core processor you should definitely consider upgrading to a multicore. However, if you already have a dual-core CPU, you probably won't gain very much by moving up to a quad-core CPU."
http://www.gamespot.com/features/6182806/p-6.html
With a 8800GTX, at high quality with a resolution of 1600x1200, the E6300@1.86 and the Core2Extremex6800@2.93 both got 26 fps. It was only after the reviewer played Crysis on low settings (medium quality, 1024x768) did he actually experience CPU bottleneck in the fps.
So at resolutions people actually play, there was basically no difference between a 1.86GHz Core2, 2.4GHz Core2, and a 2.93GHz Core2Extreme. The bottleneck here is the GPU, not the CPU.
Another example of CPU vs GPU testing in games.
http://www.gametrailers.com/player/usermovies/124500.html
I can find you hundreds of more examples for many more games. The benchmarks all say the same thing.
The latest games are GPU bottle necked. The only time you'll get any real CPU bottleneck is if you have a piss poor CPU like a 2.0GHz P4.