Ditto the Intel all the way and Win 7. There is nothing that AMD offers that can touch the Core i7's for the most part.
To add to your choices ... I would seriously look at the new Lynnfield offerings from Intel. The Core i7/i5 based on the 1156 chipset offers substantial power and heat reductions from the current Core i7 (920/950/975 Extreme) variants.
The Core i5-750 is the new entry level quad and handily bests the previous top of the line Intel/AMD quads. And at a cheaper price than the top of the line AMD quad effectively putting the squeeze on AMD. The Core i7-860 matches up nicely and can generally be slightly better than the current Core i7-920. The new Core i7-870 is too highly priced for my tastes and would instead look at the Core i7-950 over it if I was going to spend that kind of money.
The advantages the 3 Lynnfield chips offer in addition to the mentioned heat and power, is reduced price for both dual channel DDR3 memory and P55 motherboards over the previous x58 mobos and triple channel RAM.
CPU 199.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115215MOBO 139.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16813157172RAM 89.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231276Double up the RAM for 8 GB total and your full total would be 519.96 leaving lots of room for drives, PSU's etc. Add about 100 to this price for the Core i7-860 (my choice) and you've got a "kick ass" system a fair bit cheaper than the current Core i7 1366 chipset based offering.
The mobo I mentioned is just an example, you would have to research the features you require, although it does use the latest audio codec in the Realtek ALC890 which offers full 24 bit 192 KHz non down sampled blu ray audio support likely negating the need for a dedicated sound card.
Something else to chew on ...
http://www.techspot.com/review/195-mainstream-quadcore-cpu-performance/page1.html"AMD will not only be forced to decrease the price of the flagship Phenom II X4 965, but we expect them to drop many other Phenom models in the process as there's no longer enough room to offer so many different models in the $100-200 range."
"Current pricing makes the Phenom II X4 a terrible choice. At $500 against the Core i7 860, it is a bad match up for AMD."