Sakkura
Illustrious
MisterZ :
In a benchmark of a Core i5 3.5 vs a Core i7 4.0, the i7 showed an increase of 12% fps when not limited by GPU performance. However, the CPU speed itself is 12% higher (at max turbo speed), meaning that if a core i5 were clocked at 4.4, it would likely perform the same as the i7. So I'm not buying that there's any significant difference.
In Crysis 3, the i7-3960X at stock clocks outperforms the i5-3550 at stock clocks by over 28%. The two processors run nearly the same stock clocks - the basic frequency is the same, 3.3 GHz, while the max turbo (which is rarely reached in games) is 3.9 GHz vs. 3.7 GHz, a mere 5% difference. So clock for clock, the 3960X is definitely more than 20% faster than the 3550. That's despite the 3550 having a newer architecture with higher IPC. So clearly there's a significant benefit from the extra cores and hyperthreading.