As said above it would help but it would probably not make or break the system, despite the huge cost you would pay... For the i5 3570k you would need a new mobo with the z77 chip, which is an additional $100 + the time it takes to take apart your system and rebuild with new mobo, assuming you don't break anything...
You could go cheaper with a i5 3570 (no k) as this is a locked chip (no overclocking) you could get a slightly cheaper mobo and save some money on both parts, but still the cpu is rarely the bottle neck of a gaming pc unless it is less than 2 cores.