Need advice for memory and CPU cooler

Hi guys -

I'm getting ready to assemble a new build and have a couple parts left that I am undecided on... hopefully you experts will chime in and offer some guidance.

Here's what I have so far...

CM Storm Sniper Black Case
Corsair 750TX Power Supply
EVGA P55 FTW Board
i7-860 CPU
Two WD Black hard drives, 7200rpm/500GB/32mb cache (one for OS, one for games)

I'll be running Windows 7 64-bit and would like to overclock but nothing too extreme. It's my first time overclocking so I am a little cautious.

I am having a hard time deciding upon RAM. I was considering either

G.SKILL Ripjaws DDR3 1600 (PC3 12800) F3-12800CL7D-4GBRH - 7-7-7-24 1.6v
or
CORSAIR DOMINATOR DDR3 1600 (PC3 12800) CMD4GX3M2A1600C8 - 8-8-8-24 1.65v

Any recommendations as to which would be the better bet? Or am I totally off base by narrowing it down to these two? I'm not sure if I want to go with 4 GB or go ahead and get two sets for 8 GB... is there any drawbacks or limitations on this board if I fill up all four memory slots?