Don't spend money on fast RAM

Here is a very intresting test that shows that DD3 is only few percent faster that DD2 even if it is way way way more expensige:

http://www.tomshardware.com/reviews/ram-speed-tests,1807.html

"You get the best bang for the buck if you stick to the mainstream of the memory market, which currently is still DDR2-800 or 1066, preferably at low latencies. DDR3-1066 and -1333 memory do not yet result in better performance, and so should only be considered by hardcore enthusiasts, who aim for maximum overclocking performance knowing that they will get little benefit for spending a fortune."

Don't spend your bucks on fast RAM. Better invest the money is a faster video card/CPU. This way you will see a difference proportional with the amount invested!