How do I make my RAM go faster?

I have Corsair XMS @ 187.5 (150 fsb @ 4:5) with CAS 2.5/7/3/3, 2.7v.

Which speed XMS do you have that it will only run CAS 2.5-3-3-7 at the bus speed you have it at now? Try going more aggresive on the memory timings to increase your memory bandwidth scores at the bus speed it's at now.