If nVidia makes this card with watercooler and insane price to get the performance crown, AMD's answer would be simple, watercooled HD4890 X2. Not that they would do it but they could if they want to. So saying that nVidia could create a watercooled card to win over the HD4870 X2 would be a moot point.
Umm... No. A watercooled 280 trashes a watercooled 4870. There is no reason to think a water cooled 280 GX2 would not be faster than a watercooled 4870x2. Most cases SLI 280s beat a single 4870x2. At least from the benchies I've seen. And I say most cases because we all know the the SLI scaling on AoC isn't great.