Memory benchmarks
Both ScienceMark and SiSoftware's Sandra report an expected increase in memory bandwidth when moving from dual-channel DDR3-1080 to dual-channel DDR3-1800. Remember that there's a potential 28.8GB/s on tap and most of that is wasted, it seems.
The one advantage of higher speeds, given an identical latency, is a reduction in memory access time, represented in nanoseconds. This'll bear fruit when applications require constant (random) accesses to system RAM.