Would help to know what kind of SDRAM you are using, as it will likely be your limiting factor.
With only a 6X multiplier on an 800EB, you're probably going to get no higher than 900, and that's only with mongo SDRAM capable of 150 bus speed. That's at the extreme. Rock stable will probably be somewhere between 140-145, and only with excellent cooling (as you will likely have the core voltage upped significantly).