Edit: After looking carefully, I can't seem to find any DDR600 with low memory timings. Do they not make them at 2 2-2-2-5 1T? Or will it not matter? There seems to be mixed reviews on all of the DDR600 pieces.
You don't seem to understand the concept of memory latency...when you increase memory speed you have to compensate stability by slightly slowing down how the RAM handles reading and writing the data...if you don't know memory timings are basically measurements of how long memory takes at a certain point in the read/write process...if you increase memory frequency you can't maintain the faster timings and results in memory errors
The only exception to this rule would be BH-5 chips which compensate latency with extremely high vdimm...BH-5s are known to do 270MHz 2-2-2-5 1T @ 3.6vdimm with active cooling of course
for RAM listings of what will generally do 300MHz