The i7 920 is a little better. However, I would only recommend it if you play games and intend to buy 2 or 3 video cards. In that case, the expensive X58 motherboard required by the i7 920 is at least used for a good purpose.
If you are not a gamer, or can get by with a single video card, you should get the Q9550 with a GA-EP45-UD3R (or similar) and 2x2GB DDR2-800.
I believe the 920 would be a faster processor and it is also hyperthreaded...Like they said you're going to have to pay more for the MOBO and RAM, quite a bit more
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