Here's the problem with the mobo's you suggested compared to the E-PRO.
The Maximus offers no real performance increases,cost too much,and doesn't offer 333.
The Gigabyte UD6 cost more for the same performance.
The UD3 and UD4, A, models have limitations with 333 when crossfired. http://www.newegg.ca/Product/Productcompare.aspx?Submit...
Asus P7P55D E PRO will be a nice choice
It has usb3, sata 3 and also has plx bridge too. Motherboards without plx chip will cut down x16 pcie slot to x8 when using usb & sata 3.
The board also supports sli or crossfire at x8/x8