I would take a look at the extreme4 gen3 instead of extreme7, I was debating the which to pick from the two for a build similar to yours and went for the extreme4. The features are similar, here are some things worth noticing:
- Extreme7 Gen3 -
Crossfire/sli pcie 2.0 at 16x.
Only one pcie 3.0, cant crossfire/sli with future boards
4 usb 3.0 on i/o rear panel one on header.
xfast usb charging for phones and such (i think the extreme4 has too)
Dual lan ports on i/o
Only has one pci legacy port
6 sata3 ports
-Extreme4 Gen3-
Crossfire/sli with pcie 2.0 and 3.0 at 8x 8x
2 usb 3.0 on rear and one on mobo header
PS/2 keyboard port (extreme7 doesnt have it)
2 pci legacy ports
floppy connector
4 sata3 ports
Everything else is pretty even, unless I missed a minor info there, you gotta see for yourself if for your build and future add-ons if it's worth the extra 75 bucks (or more) to go with the extreme, for my build it def wasn't.