^^Get a 520hx, identical to 620hx on the 12v rail but it's cheaper.
You shouldn't plan to not overclock when it's so easy and can significantly increase performance (for ex. an OC from 2.4 ghz to 3 ghz on a Q6600 is a 25% increase and can be done on stock volts)
Wouldn't recommend SLI, either go with X38 and HD3870s in crossfire or a single 8800 GTS (and, in that case, you could just get p35)
i agree on all those
get this mobo/gpu combo
Newegg.com - ABIT IX38 Quad GT LGA 775 Intel X38 ATX Intel Motherboard - Retail
Newegg.com - VisionTek 900202 Radeon HD 3870 512MB 256-bit GDDR4 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail
get 2 video cards if you really feel the need