my bet is you'd get better, more stable overall performance at CAS 6 DDR3-1600 than CAS 9 DDR3-2000
No matter what you do, the RAM will have zero to a few percent performance change. You probably wont be able to tell without a benchmarking tool. Its not worth spending alot of money on higher speed RAM.
Current AMD architecture favors tighter timings over faster speed for
performance increase. Intel, favors neither. That said, neither makes
a significant impact on performance to warrant a major price
CAs latency refers to how long it takes the RAM to do somethign after
it's given a command. Makes no difference to FPS in gaming, but like
an SSD, it improves system responsiveness.
Stock i7-930 is 133 block, 21 multiplier and 10x memory multiplier.
Though the latter is determined by MOBO not CPU. This fully saturated
1333mhz RAM. 133block speed x 10 memory multiplier= 1330.
To OC above this you'll need to either lower multiplier or get faster RAM.
In general, we recommend DDR3 1600 RAM if you plan on a OC.
Now, the reason why we recommend G Skill RAM is that memory can
perform better than rated speeds. Most companeis sell you RAM that'll
perform at specs, G SKill tends to give you better than you pay for.
So their RAM can run at higher speeds, lower voltages and/or lower
timings than specs. OCZ ATM, is the opposite, hence we don't recommend
High speeds requires looser timings to work. I'll avoid the
tech details as to why, but suffice to say this is a mechanically
imposed limitation. Now, because faster RAM must be of higher quality
to maintain the same latency as slower RAM, they're generally better. As a result, the Trident DDR3 2000 kit that's rated at cas 9
at 2000, can hit CAS 6 at 1600 speeds. CAS 5 at 1333 speeds. This is
why people will buy extremely fast RAM. They're getting higher quality
RAM so they can run it at tighter timings for the speeds they want.
In general, considering the options you have, you can just stick with the CAS 6 DDR3 1600 kit. If you plan on extreme overclocking(over 4ghz) though, you'll want the faster RAM.