Those 320Mb cards use the old G80 core, not the G92, as does the 9800, so they handle AA terribly, tend to run hot and burn quite a lot of power for their performance and you'll have to deal with the problems inherent with SLI as well. For those reasons I'd opt for the slightly slower 9800GTX.
As a side point, why such old hardware? Current cards are far more efficient.