Ddr2 or ddr3 for dedicated server that hosts games

There is very little difference in speed between DDR2 and DDR3 although you can get much faster DDR3 memory. A 20% difference in memory speed results in a approximately 1.2% difference in system speed. The only real disadvantage of getting DDR2 memory is that if you ever want any more it is very expensive in comparison to DDR3 memory. I think in the system that you have described the real difference is in the processor being used not the memory.