980xgl is the same chip as the 8x version of the Ti4600 (ti4800?).
also:
900xgl = 4600
700xgl = 4200
fx500 = fx5200
fx1000= fx5800
fx1100 = fx 5700
fx2000 = fx 5800 ultra
fx3000 = fx5900/5950 ultra
ithere's a couple more quadro/geforce equivalancies, don't recall all of them, but if you softmod the gaming version of the card to a workstation card under one os install, you can run it as it's original gaming card under a second install - so you have dual boot: one for gaming and one for working, all at the gaming card price. (this is actually slightly more complicated than I've described, for details check out the rivatuner forum on guru3d)
in games quadros (real or modded) tend to run a bit slower than their geforce counterparts due to driver optimizations, but it's the same hardware and roughly comparable