I think what you said suits you a lot more.
The 320MB is a piece of junk, failing to run even Call of Juarez in DX10 smoothly.
It delivers- yeah right. 
Fanboy detected. 



Now, back on semi on-topic.

BioShock is an nVidia SPONSORED game, not optimized by ATi drivers or anything.
It's just the same case as Lost Planet, game devs bought over to code deliberately FOR their cards (and in this case because both cards are very different, AGAINST ATi ones) in DX10. It's not cheating, but it's obviously anticompetitive and all. Futuremark's 3DM08 should be something better to compare to- it's not a game, but it's not using DX10 half-assedly or heavily supported by either side.

Truth is, see any benchmark on Unreal Engine 3 in DX9 and it's obvious that the card you *didn't* buy wins. I did the long outlook, you did the current math. UE3 and other shader heavy titles are the major cornerstone of future games, DX9 or 10. Oh, and happy enjoying your slower card running at 90 degrees load. 
They cheated 3DMark03 with 16FP precision replacement IIRC. That does affects quality, otherwise everyone would be using FP16 instead of the DX9 FP24 standard, right?