Remember, the question at hand is "What is now the most powerful graphics card?" not which is the best bang for your buck.
The most powerful single GPU card currently available is the GTX 280.
I just think it's pointless paying $200 more for 10%-15% more performance. In fact, the 4870 even beats the GTX 280 on occassion, especially when full AA and AF is applied: http://www.firingsquad.com/hardware/...nce/page15.asp
The 4870 outperforms the GTX 280 in all of the high AA and AF benchmarks there.
Anandtech shows it winning in Bioshock, as do all other reviews:
Also, this is a great comparison between the AA image quality of RV770 vs GT 200: http://www.anandtech.com/video/showdoc.aspx?i=3341&p=11