It's funny how the same people who claimed tessellation didn't matter are now claiming it does...
Tessellation does not matter
as much for a single card because a single GTX470 for example cannot handle tessellation, while still providing smooth gameplay at 2560x1600 (OP's res. as he said). When you are talking about buying $700 worth of videocards, you aren't buying them for just 6 months. When you are spending that kind of $$, then it's fair to say that you'll probably keep them a while (in which case the extra features will come to play, and you will be able to utilize them with dual cards since you have the horsepower).
For example, we knew that 6800 Ultra could run HDR in Crysis, but it's performance was slow. However, if you were looking to purchase dual 6800 Ultras, then perhaps this extra feature would have been more of an advantage compared to X850XTs in CF. Think of it this way, DX11 isn't really a selling feature of 5770, since it can hardly provide playability in DX11 games at 1920x1080. But that's not to say that DX11 is unimportant.
OP, 5970 is an awesome card, you won't be disappointed.