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In most games you would get better performance with a quad core like an i5 760 - however for the vast majority of games the i3 540 is more than fast enough and the graphics card will bottleneck performance.
There are a few games (eg. arma2, BF:BC2, CIV 5) where a true quad core performs significantly better than an i3 dual core - and this list of games that make good use of quad cores is steadily increasing.
Therefore, my recommendation is that if don't feel you are getting performance you are happy with in games - then I would suggest upgrading to an i5 750/760. That said, may I ask what graphics card you are running?
my specs are:
intel core i3 540 OC'd @ 4ghz
msi p55a-g55 motherboard
msi gtx 460 768mb 'cyclone' edition OC'd
corsair xms3 1600mhz ddr3 ram
xfx xxx 650w modular psu
1tb sata hdd
prolimatech megahalems cpu cooler
and 1680x1050
What games do you play?