4GB vs 8GB for gaming?

I'm making a gaming computer right now, and wanted to know what was better (with gaming in mind)

Running a q6600 g0, dfi dk x38-t2rb (can handle 4x2GB for a total of 8GB), crossfire 2x 4870's.

Basically, I'm deciding whether i should get 4GB vs 8GB (of course i'll be running vista 64).

If I get 4GB, I will get 2x2GB set.
If I get 8GB, I will get 2 of 2x2GB sets OR a 4x2GB set.

I don't know much about memory so which set of RAM should I get. I know the q6600 runs 1066MHz FSB so running 1:1 ratio will require me to get pc8500 or 1600 MHz speed RAM.

Either that or do I get 800MHz rated RAM (I don't know why I would do this but I have read it in forums. Also, couldn't find any 4x2GB sets running at 1066 on newegg.).

I would greatly appreciate your opinions.

Thank you swifty - I have read this article too, and can't seem to find it to convince people.

what about for RAM speeds? 800 sufficient or 1066 the way to go?

the actual fsb of the q6600 isn't 1066, that is the quad pumped fsb. The actual FSB is 266 and the multiplier is 9 with equals the clock speed of 2.4GHz. How fast the ram will be running at 1:1 on default clocks is 266*2 = 533.

If you want to speed your ram up the you can change your divider to times 2 which would give you 533*2 = 1066 or overclock your system.

Regardless, unless you are planning on doing heavy overclocks or really want to set the divider to 2:1 to acheive 1066 memory speed, memory rated at 800MHz should be more then enough for you