More or less Ram ?

Hi, I will begin with a brief layout of my system, followed by my question.

mainboard- Asus P5K SE
CPU- Core 2 Duo E8400
Vid Card- Nvidia GeForce 9800 GTX
Memory- up to 8G @ 667/800/1066 MHz (dual channel support)

Question: For high end online gaming, which memory combo would perform better?

4G @ 1066MHZ or 8G @ 800 MHz

Thanks in advance