i would pick up a x1800xt any day for $299 over a 7900GT. but unless you wanted a cheap sli then its another story : )
1x X1800GTO = if the peformance is better than 7800GT then its a great card for $249
1x 7900GT = awesome if x1800xt aren't at $299
2x 7900GT SLI = awesome $600
1x x1800XT = better than a 7800GTX in my mind and would be awesome for $300
1x 7900GTX 512MB = blah for $499 :! x1900XTX will be still overall faster
2x 7900GTX 512MB = great for $1000 :! not awesome but great
1x X1900XTX 512MB = $499 Awesome and better than 2x 7800GT Setup
1x X1900XT 512MB = $450 Awesome and better than 2x 7800GT Setup
x1900 Crossfire setup = $1099 Expensive but best money can buy unless you are going quad sli or dual core gup sli. RD580 mobo are great and better than current SLI motherboard in my opoion
well it confusing but a nice price war will start arround 9th march

Nvidia may need to do something more because a performance isn't great in the G71 series :!