CPU or Graphics Card Bottleneck?

[Flying_Nut]

Hi guys,

Still lost in the mire of graphic card upgrade paths!

A question for you please:-

I currently have two 6800GTs in SLi config and an A64 (Winchester core) 3500 CPU. I overclock the latter by 5% using Gigabyte Easy Tune utility when I want to play graphically demanding games such as Fear etc, although I'm limited to a max res of 1280 by 1024 on my 19" monitor.

Which would give me the best return upgrade wise please, replace the two 6800GTs with a single 7900GTX or upgrade the CPU first to say a dual core 4400 or the like?

Thanks in anticipation of sagely words of wisdom!

 

[Flying_Nut]

Is it better to have a 24/7 overclock or only when you need it? Thought it would be better not to stress the components when browsing the web or working in Photoshop CS2 etc?