The 4-core is better since raw process power from each core is higher it can finish tasks faster, but the pipelines of the CPU matter, its architecture(22nm), its instruction sets.
Since windows cant use all 4 cores correctly(heck it cant even use 2 cores correctly) you wont see much improvement in terms of speed but in any modern game.
The games engine can handle 2 cores, so if you get a quad core you will have 2 cores idling.
If you use a program like FRAPS to record your game play make sure you set affinities so your game runs smoothly and you get a good recording
Eg Set your games to run on CPU Cores 0 and 1, and set FRAPS to run on cores 2 and 3.
You can set affinities manually with batch files or use a program to do it for you.