Currently, i know of no games that increase by a considerable amount (more then 1 FPS or so), which is why i voted for only memory bench progs.
The same can't be said for programs that make heavy use of memory, such as encoding ones, though:
This is with a PL of 6
This is with a PL of 7
The above tests were conducted on the same movie: i only changed the PL, the multi and FSB (and some voltages: different ones in one or two instances).
Had i used a PL of 7 for both, the disparity should be even bigger, i believe.
That's slightly over 6.5% reduction: from 757 seconds to 707 seconds!
It's a significant number!!