HotHardware.com evaluate the features and performance of three X48-based motherboards. And it looks like the ASUS Rampage Formula is the best one. Here's a bit:

ASUS Rampage Formula: In typical ASUS fashion, the Rampage Formula was a pleasure to deal with, from the installation of the board, to its stable operation, and better yet its strong overclocking. ASUS really targets the PC enthusiast market well, providing features that help their boards stand-out from the rest of the pack. Whether it's powering up the system from clearly marked and lit power buttons, diagnosing system issues with the LED poster, or overclocking the board with the ample options in the BIOS, ASUS is almost always on the ball.

We managed to hit a 520 MHz FSB while overclocking the Rampage Formula, and while that might not be the highest speed attainable due to the memory we chose, it was clearly faster than the competition. The bundle is first rate, even going so far as to include a retail copy of S.T.A.L.K.E.R., the aforementioned LCD poster, and a branded and labeled I/O shield, for people who like those kinds of things. Pricewise, the Rampage Formula is the highest of the three and will set you back almost $300 dollars, but it's money well spent if you're in need of a high-end Intel-based motherboard.