Maximum PC tests and answers the three biggest questions you have about RAM: How much better is DDR3 than DDR2? Is high-speed RAM worth it? How much RAM do you really need?
On the DDR3 question, with AMD's latest AM3 Phenom II chips, they found no difference between DDR2 and DDR3. Which is good, since DDR2 memory is way cheaper than DDR3, meaning you can buy way more of it.
Going from DDR3-1066 to DDR3-1600 RAM generated some real results in some instances—slight boosts in gaming—with the Intel's Core i7 processor, but DDR3-1066 is still just fine.
And yeah, more RAM is still better, though you can get by on 2GB of RAM if you just do one thing at a time. But who the hell does that? Check out the full testing gauntlet and article, which is packed with other RAM trivia obscura: [Maximum PC]