What are you plans for the future of your PC? are you planning on going with SLI in the future?
The 750W is more power than you need for a single GPU system, the Be Quiet Dark Power are better
http://www.overclockers.co.uk/showproduct.php?prodid=CA-021-BQ&groupid=701&catid=123&subcat=1083
a little more money though.
do you plan on overclocking? is so the Asus P6T Deluxe is a better board, but isn't necessary. The P6T SE will do perfectly, and can sustain a 4GHz over clock on the i7 920.
I'm running on a P6T which supports SLI where the P6T SE doesn't. both of these boards are slightly less than the EVGA and are goo boards. and relitively well layed out.
the gainward card is nice, the custom cooler is supprisingly quite, but it does make a noise after some heavy gaming sessions. i'm running the GTX275 version and i'm very happy with the results. I've got the same D0 stepping i7 920, 6GB OCZ Reaper PC3-15000 (1866), and the gainward GTX275. and Crysis runs maxed out in windows 7 as smooth as.
well thats my limited advice, hope that helps.
in answer to should you wait to buy them with windows 7, well thats always the question, should i wait a little bit more and the parts will be cheaper. it all depends on how much you want your new pc