Cal, you may be stressing your memory controller out a bit with those tight timings. I know with my OCZ Rev.2, 265MHz is on the borderline stable at 2.5-3-3 timings. Give 2.5-4-3-7 a try, you may have better luck, and won't loose too much in your sandra bandwidth. Also, what memory voltage are you using? Give 2.8-2.9 volts a try. I would not be surprised if you can run 9x290MHz with 2.5-4-3-7 timings. If you find that unstable, you can even try 2.5-4-4-8, which is easier on the memory controller. But with 290MHz, the slightly looser timings do not outweigh the increase in frequency. I have been struggling for a quite a while trying to find a good balance of mem-frequncy and multiplier, however my winchester memory controller is rather poor, and I am limited to an 11x multi if I want 100% stability. I can do 305x8 without any problems at 2.5-4-3-6, however that only gets me about 2.4GHz. As soon as I start pushing the memory frequency past 250mhz with a 9x or 10x multi, I cant get the system stable. 10x260 works for me, but I have to use 2.5-4-4-8 timings, and it is still not 100% stable. HL2 deathmatch has been the ultimate stability test for me. I can prime overnight no problem, but I could not get through more than an hour or two of HL2 DM.

Good luck! You are far from the limits of your gear, keep pushing! Those 4000+ chips are usually pretty solid.