SupCom upgrade: i3 540 OC'd or i5 2500k for more $?

I've been trying to do some research..it seems I can get an i3 540 and make it run @ 4ghz and get like i7 940 performance.. for about $350 total...do you think this would be A.) run near i2500k stock with my GTX 460..or B.) should I just wait and get into i2500k for about $480 total?
My major dilemma is game speed in RTS like SCII, Supreme Commander and Sins of a Solar empire.
If I can match the game speed of a stock i7 940- that would greatly increase my game speed bc those games are very CPU dependent...the games starts out fine..but after thousands of units built..the game speed will slow down in the negative for my meager 2.8 GHz Phenom 2.
I have considered buying a new motherboard to OC the Phenom II, but I will still have to buy Windows 7 system builders (bc my Windows 7 copy is tied to an OEM motherboard) and it still won't be as fast as Core series CPU.
So the question is: Can I go cheaper with Core i3 540 and still get the gains I need or will saving-up the extra $130-140 for Core i2500k just blow the doors off of it?|||Lightman|||I suggest you get some simspeed "facts" from people with those fast CPUs.
PS: I remember that MB cache had some effect on simspeed on Supcom series but i am not sure |||I went from a QX6700 Extreme to a i72600K, difference in all apps is insane. My GTX 480 is too slow for this beast. Amazing CPU.