It depends on the games as to which gives better performance. If you plan to overclock the 760 would be better, otherwise the i3 has upgrade potential (but if not upgrading within a year Haswell will be ouy on a new chipset anyway) and uses less power and has much better perfomance when only 2 cores are used.
well it all depends on your budget, if you have no problem with budget then go with i5 2500K a Z77 chipset motherboard (either AsRock for the cheapest decent one, then Gigabyte, Asus, or MSI are the bigger brand out there)... then go all out with the GPU (like HD 7870, HD 7950, GTX 760, or GTX 770). Although that will be about $800~$1000...
or maybe you can go with i3 3240 + h77 chipset mobo + GTX 650Ti Boost (around $350~400 ish) ???
i5 750 without hesitation. 4 true cores..clock to 3.8-4.0.
Much better;IPC is a little less,but 4 REAL cores and overclocking makes it better.
You won't be able to run bf3/gta4/arma well on a dual-core cpu.
Clarkdales still are the dual-core champs on HWbot because you can't overclock newer duallies very far.