if you are using 2 dimms you are more likely to lose stability by lowering the cas timings, as you have 2 chips one may not yeild as high as the other, if you lower the cas latency you will usually only crash when booting into windows, or during 3d operation. So if you crash as a result, you just got back to cas 2.5 and all is well, for better success with this i reccomend one chip.