You dont want to go ATI (AMD) but you dont mind going AMD for the cpu???!!
AMD are so far behind nvidia in the cpu department it isn't funny, go with intel, either the 8400, or if you are gonna use some apps that can use a quad, the q6600 or faster.
ATI currently lag behind nvdia but not by too much. Also in june the 4870 will be launched which will at least for a little while be the fastest gpu around. If you cant wait then go with the 9800gtx but with the understanding that it is based on an old design and come this summer will be made to look rather poor compared to the ATI's and nVdia's new offerings.
The Q9000 series are not a massive step up from the Q6000; the larger cache doesnt make much difference in the real world. The Q6000 offer better price/performance especially if your going to OC....but as your not then just go for the most you can afford.
Two 8800gts are a better bet than the ultra, but as i said, the new cards are just round the corner and will definitely offer a big step in performance. IMO i would just get a card to tide me over until the ones appear and then i would upgrade (evga offer a step up program). The 9600gt (<£100) would be good for now.
What games do you want to play and at what resolutions?
A single 9600gt can deal with any current game (except crysis) at 1280X1024. Spending the extra 160 on 2 88800s would only get you more fps on these games and still is a bit lacking when it comes to crysis.
the q9000 is a 45nm and degrades much more rapidly when you increase volts.
LoL WTF? 45nm's are COOLER, More Efficient, and have More overclocking headroom. Simply put, they are the best technology as far as processors go AT THE MOMENT. They can take more +Volts then any other core out there, but thats not why they're good;; Its because you can OC a TON without +Volts.