There's a rather handy comparison here:
http://www.anandtech.com/bench/default.aspx?p=81&p2=52#
The current heirarchy at around this price point appears to be:
CPU____________________
Individual___
Bundle (CPU, Mobo and RAM)
Intel i7 920________________£242___________£500
Intel Core 2 Quad Q9550_____£212___________£398
AMD Phenom II X4 940_______£192___________£370
Intel Core 2 Quad Q9400_____£186___________£372
AMD Phenom II X4 920_______£160___________£338
Intel Core 2 Quad Q8200_____£132___________£322
It should be noted that the performance increase is pretty small from the Q8200 to the Q9550, while the i7 is miles out in front. The big benefit of the i7 is that is a little more 'future-proof' than the others, and it overclocks well (I'm happy to OC) any thoughts on where the value points are in that little list? The only thing I can see that is glaringly obvious is that the Q9400 is overpriced.