256+512mb issues on Epox 4BDA2+

I have an epox 4bda2+ (i845) motherboard with a p4-1.6GHz @ 2.13Ghz. I initially had the system with Muhskin PC2700 256MB running at DDR354. The system was running for about a year with no problems. Then I decided i needed some more memory. Since the motherboard only has 2 ddr slots, I decided to get a 512mb stick. I managed to get a hold of the corsair xms 512mb pc3200, therefore, I assumed it would do DDR354 with no problems. I inserted the ram and booted up the system. The system booted up fine but when i went to play some games, i noticed instability. It would exit out of the rallisport game with no errors mulitple times..and it would crash while playing the call of duty demo. The timings were 2.5-3-3-6. I immediately ran memtest 86 v3.0 and it didn't detect any problems so i was clueless. Then i tried running the Corsair ram by itself and it ran fine at cas 2 and cas 2.5. Then i tried the mushkin by itself and it was fine also... Now i have them running together again but i bumped the voltage up to 2.7v. It seems to be stable, and i haven't experienced a game crashing yet (knock on wood). Anyone know why i was having a problem with these sticks together at 2.6v? Also, is there any other program out there that i can use to really test the stability of the ram? Thanks.