Using SiSoft Sandra 2010 benchmark for Memory Bandwidth, the difference between the DDR3-1333, shown on the left, and Crucial DDR3-1600 on the right, is almost 10%, increasing from around 13.6GB/s to more than 14.8GB/s.
When measuring the memory latency however, the lower timings of the DDR3-1333 show a slight advantage over the Crucial DDR3-1600, although the difference is practically negligible.
Benchmarks will typically indicate a measurable difference however when in real world comparisons they are practically the same. Using SuperPi to calculate the value of Pi to the millionth digit does reveal a small improvement to the faster Crucial memory, however we're talking about a tenth of a percent difference.
Likewise in Futuremark's 3DMark06 the difference is once again minuscule, only a tenth of a percent, although it again shows a small improvement in the faster Crucial memory.
3DMark Vantage reveals that when more emphasis is placed on the graphics processing, even the difference between 2Gb of 4Gb of memory has little effect.