Then why not save some cash and get a second 5970 (which you may not need) later when it's cheaper?
Also, why don't you skip the 975, get a 920, and upgrade the board to the regular P6T, then overclock? My 920 reaches 3.7GHz without a voltage increase on a P6T - when I've more time, I'm going to see what it takes to get it to 4GHz, but I certainly know I can do it. The performance will be the same, and more impressive since you did it yourself.
Edit: Also, for OCing, you should think about DDR3-1600 memory, but with the 920 1333 might be enough.
Edit2: Just to put it in perspective, my two 5870's (which are just a bit stronger than a 5970) can max any game playably at 1920x1200. Most of them are well over 100 and 200 fps.