Testing on both AMD and Intel desktop PCs has shown that with DDR3 RAM there is little to no tangible performance gains in real world applications on desktop PCs once you get above ~1333 MHz.
AMD Llano/APUs are the exception as both the CPU and GPU can access the higher frequency and that does improve real world performance. Increased frequency is best with the APUs. Latencies don't make any tangible diff.
As the frequency increases one clock cycle becomes less and less in real time. Since the DDR3 RAM isn't a bottleneck there isn't much to be gained. Some folks have OC'ed the FX CPU RAM to 2400 MHz. and seen ZIP for performance gains because the RAM is not limiting performance.
Benches will show a little improvement
but that doesn't seem to transfer to real apps. for most folks.
Intel has even announced they will stick with DDR3 until 2014 because it's not a bottleneck.