Help - Memory/System Upgrade - PC 6400 or PC 8500 on 780i w/ E8400

I've got a quick question for everyone. I did try to figure this out for myself, but trusted that some of you out there might have some experience with it.

I'm building a computer for my father-in-law and ma switching out a lot of my components and getting new ones for myself.

I've purchased a new E8400, a new 780i (MSI - yes, I plan to SLI in the near future), a new 8800GTS, and even a Tuniq Tower so I can overclock the E8400.

My question is this: (please keep in mind that I want 2x2GB sticks)

What RAM should I get - I'm down to Crucial or Corsair ? (supported by the mobo manufacturer)

PC 6400

CORSAIR XMS2 DHX 4GB(2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) - 4-4-4-12

http://www.newegg.com/Product/Prod [...] 6820145194

Crucial Ballistix 4GB(2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) - 4-4-4-12

http://www.newegg.com/Product/Prod [...] 6820148183

OR

PC 8500

CORSAIR DOMINATOR 4GB(2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500)

http://www.newegg.com/Product/Prod [...] 6820145197

I was thinking the smart thing to do would be to get the Corsair PC 6400 - especially with the cheap price, but I have had good experience with Crucial. Then I was thinking the Corsair PC 8500 would be great, and it's a decent price and includes the memory cooler.

I was wondering will I ever need the extra speed of the PC 8500, or will the PC 6400 do?

Please let me know what you think.

Ok...just Dominator vs Ballistix.

Now the questing comes down to do I need PC 8500, or will the PC 6400 be enough. Plus the Dominator comes with the Memory Cooling Fan.

Will I even notice a difference between DDR2 800 or DDR2 1066? Either way, there are fantastic deals on both sets of 4GB kits.

Any help would be nice.