One GTX 570 is a good match for your CPU at 3.6Ghz, but two is too much GPU for that CPU, but even so a Q6600 @ 3.6 should be enough to provide your cards with a playable frame-rate on just about anything. Unless you want to use 3 monitors I say go with two GTX 560 Tis instead and save a little money to upgrade the rest of your system when Ivy Bridge and Bulldozer are out, or whenever you feel your CPU just ain't cutting it anymore.
I used extreme PSU calculator and for my OC and the two 570's I'll need a 1085w PSU, so... I think a 1500W could be enough for a long time...
Ok, so two 570 it's too much for my Q6600... I will go for 1 570 and then soon I hope, change my CPU/MoBo/Ram and then think about a sencond 570, thank you so much.
Well, I don't know... i went to http://extreme.outervision.com/psucalculator.jsp, and use this settings:
High enf Mo B
Q6600 G0 with OC (3600MHz/1.55V = 219w)
2 Sticks DDR2 SDRAM
Regular SATA x 3
1 DVD/DVDRW Drive
80mm regular fan x2
120mm regular fan x 4
120mm led fan x 1
swiftech MCP655 x2
20% capacitor aging
and a 100% CPU utilization and system load for worst case scenario... Minimum PSU Wattage : 1055w
and that's why I think I would need a 1500w PSU for no future worries...
1500W PSU definitely still seems like overkill, even for future-proofing the system...
Also, 2 x GTX 570 would be a waste with a CPU like that. At 3.6 GHz I suppose 1 would do fine, but don't bother to SLI it. By the way, 1.55v is a VERY high voltage to be running the Q6600 at. You should try lowering it if you wanna preserve the CPU
I just have to back up what other people have said. 1500 is absolute overkill. Im running 1 570 on a 600w and no problems. With just a bit more I could do SLI. Save some money there and upgrade you mobo and cpu.
I know people are saying the 1500W is overkill, but if you really want the 570s then I think it's a good idea. After all, if the setup is going to draw 1055W then that would be using 70% of the 1500W units capacity. Of course, that's really only worst case so a 1200W might be a bit more reasonable (1055 would be about 88% of it's capacity). The less you stress your PSU, the cooler it should run and the longer it's life should be.
I still say that two 560Tis would make more sense because your CPU would limit that setup anyway thus giving you the same performance in your rig if you had two more expensive 570s. It would also allow you to use a cheaper PSU ^_^. It's up to you.