If you're dead set on an nV card, then go with the FX5900XT/SE/EPV/LV/etc.
They are far better performing than the FX5700U, and even in DX9 titles it's competitive with the R9600XT.
Here' two good reviews from [H] that show the diff;
<A HREF="http://www.hardocp.com/article.html?art=NjA0" target="_new">http://www.hardocp.com/article.html?art=NjA0</A>
<A HREF="http://www.hardocp.com/article.html?art=NTk5" target="_new">http://www.hardocp.com/article.html?art=NTk5</A>
Hope that helps.
Still think the R9800 is a better deal, but the FX5900 should be ok.
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