Corsair xms3 1066 DDR3 upgrade?

[lynd20]

I have a asus P5K3 D motherboard with 4x 1gig corsair xms3 1066 DDR3 memory. I would like to upgrade this. Would I be better to go to xms3 2x 2gb 1333 ddr3 or as my mother board supports it go to 2x 2gb 1600 ddr3? I have a q9650 with windows 7 64bit which I'm planning to overclock. Or any other sugestions are welcome please.
Thanks

 

[Yellowbeard]

If the prices are similar between 1333 and 1600, I'd suggest the 1600 2 x 2GB. That will give you a bit more headroom on memory frequency. But, the 1333 will do well also.