Bit-Tech published a look at Intel Core i7 Memory Performance using Corsair's Dominator TR3X6G1600C8D memory.

Intel has made a system that for the most part alleviates the need for more memory bandwidth. Three channels of DDR3 means we're saturated with it from the word go, and for the most part spending big money on faster performance memory has a unnoticeable effect.

For games, it does nothing in the real world because the bottleneck is firmly elsewhere: either the threading capability of the game, the clock frequency of your CPU (not the Uncore) or the graphics subsystem. For other things, we're still limited for stuff like IO and storage bandwidth - so while people complain about memory use, having programs use up a big chunk of 6GB (or more) benefits performance because we're not limited by measly hard drives.

In the one important scenario - multi-tasking - the performance benefits are more considerable, so if you're heavily into running many things at once (partly what the Core i7-X58 combination was designed for) then there is likely a performance benefit in store for you.

Basically, we feel the best advice is don't go crazy because the benefits in the real world are generally not there and are better spent elsewhere. Buy memory that supports your CPU overclocking: but even if you run a base clock of 200MHz on a 6x multiplier from a Core i7 920, the memory can run at 1,200MHz so you don't need the full 1,600MHz.

Intel Core i7 Memory Performance