?'s on a P4PE

The turbo option for the system(not the memory turbo), exactly what does this do? I see that it raises the FSB and Memory by 2, and noticed that it put the DRAM idle timer to 64 instead of 16, but what else does it do? I ask because it made only my games unstable, but nothing else.

Also, which is better to run the memory 3/4 or 4/5. I can only select either 355(3/4) Memory or 333(4/5).