Well assuming you're not going to overclock the Q9550 will be faster for most things because of the higher clock speed, but anything multithreaded the i5 should walk all over it as it's actually a proper quad core as opposed to 2 dual cores stuck together. If you are going to overclock, definitely the i5, if the i7 is anything to go by these should easy to make incredibly fast. 8gb of ram is probably a little overkill for gaming by the way. Either way I'd probably go for the i5 just cause i love my i7 so much.
Desktop: i7 920, GTX 275, asus P6T, antec 1200, 6gb ram, 1tb spinpoint f1, 1tb spinpoint f3, Logitech Z2300, Zero DAC, Shure SRH440 Laptop: Toshiba satellite, T5300, Go 7300 Home Theatre: 32" loewe CRT, Harmon kardon amp, dvd player, image 418 speakers, rega planar 25 turntable :)
I had my first experiences with triple channel ram the other week in the new G6 HP servers. Very fast RAM as long as you set it up correctly. I take it you are talking about triple channel kits and dual channel kits to make up the 6Gb and 8GB sets?