I'm running a 3400NC on a DFI 250Gb with a XP90 just like you. I had a gig of Mushkin 3500 LII in it and couldn't get it to clock up that well. Put in a set of OCZ 3500 ELGX and have it running at 2.7 with my ram at 1:1 2-2-2-5. I had to use a divider with the Mushkin to get the clock speed up. From what I've read on DFI Street.com, it's better to use a ram divider and get a higher cpu speed with the A64's. Might want to go there and check it out. Btw, I had this up over 2.9 but it wasn't stable. Couldn't quite get 3.0 though. lol