A big-dollar rig, huh?
A 3770K - Tom's questioned why anyone would need more than a 3570K to do anything at all!
So it's a great CPU of course, probably more than anyone needs (but I like i7 myself).
And 2 x 7970!
I would never advise anyone to put a lot of money into Radeons.
Two nVidia cards will give much better results...
Anyway: motherboards used to support either CrossFire or SLI.
Now, most mobos will support both so this isn't a major consideration.
I personally would select a top-quality mobo from either Asus or Gigabyte; anything with the Z77 chipset.
Probably full-ATX, though many Micro-ATX mobos can run 2 vidcards these days (if you're into small).
Gigabyte GA-Z77X-UD3H is good, at around $145 bucks.
Or, Asus has all kinds or different P8Z77 mobos - I just used one for a 3570K Mini-ITX build. Sweet.
I use Gigabyte for myself - but usually Asus for other people!
Asus is by far the friendliest, bar none...
When you check for a BIOS update they never ask you "what version of the motherboard do you have", LoL, like Gigabyte does.
But (if you're handy) I believe Gigabyte ultimately is the best.
My recamend is fill all slots dont see capacity. see mhz in board and ram.Reason mhz is the key to achive speed. if board support 1600mhz u insert 1333mhz its waste because not get full speed of ram slot. if board support 1333mhz u insert 1600mhz its also waste of money (1333mhz ram is cheaper than 1600mhz)also u not utilise full speed of ram. (2x4Gb=8Gb 1600mhz=3200mhz =3.2ghz) vs (2x8Gb=16Gb 1333mhz=2666mhz=2.6ghz).
U r board supports above 2000mhz ,so buy transcend axeram 2133mhz *"oc enabled"* with lifetime warenty so future proof.