lol it seems to me you really want the x1600pro. just go for it. the x1600pro is FASTER than the 6600gt, but slower than the 6800gs. for the price you listed at ncix, seems like a good deal.
i've found benchies of the x1600xt raping the 6600gt, and almost on par with 6800gs peformance, but i did not find benchmarks for the x1600pro, for that, i'm willing to risk my rep (lol..) and say that the x1600pro is faster than the 6600gt. (if you wanna make me look bad, show proof).
since the x1600pro is cheaper than the 6600gt, go for x1600pro. unless you're a heavy gamer.. then spend extra (not really worth it..) and get the 6800gs
"Is virtue a thing remote? I wish to be virtuous, and lo! Virtue is at hand." -Confucius