Dunno if this will help you, but I had both a 3Ghz Pentium 4 and a 2.66Ghz Dual Core recently assembled.
With regard to FarCry 64 bit, mas kusog ang 3Ghz. The unit, though, sige'g overheat until I installed 3, yes count them, 3 Antec fans.
Ang 2.66 Ghz, wala'y problema sa overheating even with only 2 fans.
This is what I understand so far: For gaming alone, go for processing power. For multi-tasking, go for the multiple core.