Which RAM for gaming?

Hi, for the bus speeds, hardware, etc please see below but my basic question is which of these would perform best for gaming?

2 x 1GB DDR2-667 OC'd to 800MHz (matched pair in dual channel mode)

1 x 2GB DDR2-800 native 800MHz

1 x 2GB DDR2-800 OC'd to 1066MHz (if stable)


Additionally I know that 2GB is minimal these days for a gaming rig but until I can afford an upgrade am I correct in thinking mixing the RAM would result in lower performance all round, even though I could total 3GB with my 2 slots?

Many Thanks!

Details:
Gigabyte G31M-ES2L motherboard
Intel E7200 2.53GHz OC'd to 1333MHz = 3.16 GHz
Matched pair of 1GB DDR2-667 Kingston modules OC'd to 800MHz