RTS games are slightly more CPU bound and benefit a bit more from a larger L2 cache, but if you mostly play FPS games, then the extra money spent on a bigger L2 isn't worth it and spending the money on a better GPU will bring better gaming performance.
As we can see here: http://www.tomshardware.com/2007/09/...ore/page8.html
an overclocked E2160 is comparable to a stock E6750 in games.
You might also want to consider the 5000+ X2 Black Edition which features an unlocked multiplier and can be overclocked to 3.2GHz with a simple multiplier change, and 3.4Ghz with a bit more tweaking. It goes for around $89: http://www.newegg.com/Product/Produc...82E16819103194
Modern and future games are much more GPU dependant so it's not worth spending loads on a CPU if the PC will be used solely for gaming.