I'm pretty sure it's 800FSB, not 533FSB.
800FSB on a x9 multi is actually pretty much the 'ideal' multi considering what current Conroes are doing.
If you can manage to double the clockspeed to 3.6GHz you are still doing a 400FSB (pre quad pumped of course, 1.6GHz effective), almost every single 965/975 board can do that no problems. On a 1:1 mem/FSB ratio that would mean DDR2-800, and pretty much all DDR2 on the market nowadays can overclock to DDR2-800 speeds.