So over the next week or so, I'm going to be ordering my new computer(

). I've decided on all but a couple of things.
The first one being the motherboard. Yeah I know, ordering a new computer but not being decided on the motherboard is noobish. Go ahead, say it...... But they are very similar as far as I can tell. And i'm mainly concerned with the reviews on each from people who have actually owned/used one. The two in question are:
Gigabyte GA990FX-UD3
ASUS M5A99x EVO
It will be either one of those two boards. The reasons I picked them are A: Both seem to be capable overclockers; B: Both support at least 2-way Crossfire/SLI (not that I'll be using either right off the bat); C: Both seem like a stable platform on which to build a gaming rig. I'm just looking for some opinions more or less, or some blatant flaw that I have overlooked.
Um, on a side note. I have another inquiry about my power supply. I currently have a Corsair GS600 PSU, its about 5 months old. Maybe 6. IF I'm building a new system, should I order a new power supply, or is the one I have still plenty good enough?
Thank you all for the input.
Edit:
AMD FX4100 CPU
Asus M5A99X-Evo mainboard
XFX Double-D Radeon 6870 GPU
GSkill Ripjaws 8gb DDR3 PC3 12800
Crucial M4 64gb boot drive
Segate Baracuda 500gb Storeage Drive (will be adding a 1tb in the future).
Primary use will be as a gaming rig