i have the tforce 550 se (bought from newegg; it's listed as 550, they don't distinguish so i'm guessing they only sell the se now. i checked biostar's site and the only apparent difference is the se has 8 ch audio and the original has 6 ch) and a brisbane 3600 at 2.85ghz (9.5x300). the processor won't go any higher, but i know the board will because i lowered the multi and raised the fsb to test (haven't gone to the limit but i know it hits at least 315, probably higher since i haven't raised any of the voltages besides cpu and mem, so it should be as fast as you'd ever need for a brisbane 3600). however the dfi is also a good option; it's your call.
edit: uh, i just looked up the specs for the dfi, get it. firewire, sli, 2 pata ports, optical s/pdif out...get it! i wish the tforce 550 had 2 pata ports (never know when you'll get a good deal on a pata hard drive; i just got 2 400gb seagate pata drives, one a 7200.8 and one a 7200.10, for $90 shipped, both factory refurbs still with the factory seals in tact).