I agree with above and every time I see buying components before a CPU is released often ends in disappointment. There will be kits, more than likely, with both XMP and 'SPD' that are tailored and tested for the IB.
All I know is that the IMC is similar to the current SB-E and DDR3-1600 is added to its base frequency.
The 1.35v RAM kits, my experience with my 8x4GB (2 kits) of Vengeance is they're great at both Rated (manual) and XMP, but the couple times I tried to OC to DDR3-1866 ended-up in post failures. note: at the fraction of time I was testing my Sabetooth X79 was diying a fast death so I didn't need a complication. My general experience with Vengeance is that their IC's are not in leagues with Dominators and OC'ing 8 sticks is a boat load different than 2 sticks. However, the 1.35v kits I had gave me the best numbers I've seen from a DDR3-1600 CAS 9 kit.
Therefore, if I had to buy I'd probably look at an X79 kit DDR3-1600 CAS 9 and if not OC the RAM the Vengeance but OC'ing the RAM defiantly the Dominators. Further, as mentioned the 1.35v are indeed more expensive, but they are also the easiest on the CPU.