the intel build will smoke the AMD in terms of performance.
Why are you going straight in with 2 cards though? a single more powerful GPU will offer similar performance but MUCH better upgrade potential (since you can drop in a seond din the future when prices drop)
also, the amount of RAM is overkill, and the PSU is WAY overkill. you could power 4 cards on that. a decent quality 650w PSU would be more than enough. just make sure its from a reliable brand like corsair or seasonic.
the point is you just spend the same ammount. whatever you are spending on those two cards, spend on a single card of the same price but higher performance.
yes, its may perform slightly worse (but will at least be consistent, which certainly can't be said of multi card setups) but it means you will be able to upgrade sooner, for less cash and get more performance. (3 card scaling is considerably worse than dual card)
as for the PSU, it depends on what 3 cards you want. but a decent 850w will power any two High end card, or 3 lower end ones (easily 3 6850, it would probably handle 4 of those)
Motherboard: z68 mobo
GPU: whatever video card you want with all the money u saved
Ram: 8GB DDR3 1600Mhz
HDD's: 1x1TB 7200Rpm,
this will go as fast as the i73820 setup in games which is what im assuming its for by your gfx setup and totally beat down anything from amd and with all the cash u save u can buy any video card on the market. KW power supply is overkill and 8gb is enough ram at the moment and is easily added later if need be
Is this a reasonable motherboard if I went for your "Third Setup", ASUS Rampage II Gene ROG
thats high end kit, i would only get it if you have money to waste otherwise there are plenty of mid range boards to choose from i also noticed they are selling the z77's now too, the asus z77 sabertooth looks like a nice board