If you can afford the price, go for the Rampage III.
It supports DDR3 2200(O.C.)/ the other one only 2000Mhz.
The rampage supports 4 x PCIe 2.0 x16. You can install 1 graphic card at x16; two at x16/x16; three at x16/x8/x8 and four at x8/x8/x8/x8 configurations.
The Premium supports 3 x PCIe 2.0 x16. You can install even three graphic card at 16/x8/x8 or x16/x16/x1 mode.
The rampage has also the JMicron JMB363 PATA and SATA controller:
1 xExternal SATA 3.0 Gb/s port (SATA On-the-Go)
1 xSATA 3.0 Gb/s port
The rampage overclocking extremely well. It has
- 8-phase CPU power
- 3-phase QPI/DRAM power
- 3-phase NB power
- 3-phase Memory power
- ML Caps on CPU, Memory and QPI
....
The ASUS P6X58D premium is a great mobo, but the Rampage III is a dream.
Anyway, as some other people have said before, if you don't go for the Rampage, I would go for the P6X58D-E. It's cheaper than the premium and performs very well.