Native frequency of RAM modules is *quite* important aswell - the higher the better. As far as capacity is concerned - the more you have the more you'll load.
Not really, the memory clock speed dictates data rates, however it's useless to pick ram that has a higher clock rate than of the memory controller, as the memory controller would bottleneck the data transmission.
what differentiate ram performances is the CAS latency labeled as "C#" where the # is the first of the series you see bellow, ie the corsair set is a ddr3-2400 C10, by opposition the official standard (jedec) latency for ddr3 1600 is 9 hence the name ddr3-1600 C9.
Best Timings at 1.65 V . ................................
DDR3-2400 .................
DDR3-2133 .........
DDR3-1866 ......
DDR3-1600
Corsair Dominator GT CMGTX8 (4 x2GB) ...... 10-12-10-12 ................ 9-10-9-10 ............. 8-9-8-9 .......... 7-8-7-8
G.Skill Ripjaws Z F3-19200CL9Q-16GBZHD......................................... 8-10-9-10 .............. 7-9-8-9 ................ 6-7-7-7
Geil Evo Corsa GOC316GB2133C9AQC ........................ ........................ 9-11-9-11 .............. 8-9-8-9 ................ 7-8-7-8
Mushkin Redline 993997 .................................... ............................. 9-10-9-28 ................. 8-9-8-9 ............ 7-8-7-8
If you take a look at benchmark again knowing that the g.skill has thee lowest latency, you'll see that it does have marginally better performances in the 1600 test, but that it can't be differentiated form the others at higher speed because the memory bus is saturated.
Then you might ask why vendors are pushing those module?
the reason is called overclocking. When overclocking, you raise the motherboard base clock, The ram and the cpu doesn't have clock generator, they rely on the motherboard's clock and simply set their speed with a multiplier, Meaning that if you raise the mobo's clock (do an overclock), ram will run at a higher speed than designed. Knowing that your module are certified to run stable at a higher clock rates means that they won't limit your overclock, or at least not until you reach the base clock they're certified to run stable at.
sources:
http://www.tomshardware.com/reviews/quad-channel-ddr3-memory-review,3100.html
