It'll work, but your powerdraw could easily be 450w and upwards.
http://www.extremetech.com/art.../0,1697,2253572,00.asp Check out the 3d and CPU load for a single 8800GTS 512mb. Also check out this review:
http://www.hardwarecanucks.com...-x2-1gb-review-14.html with a load of 338w on a single 8800GTS 512mb. Add another one, and we'll definately see 400w and more. Anandtechs review showed quite different numbers though:
http://www.anandtech.com/video/showdoc.aspx?i=3209&p=12 . Which was the reason I was a little weary to post, because I simply don't know for sure. I don't know how exactly anandtech measured the power draw, by perhaps running BioShock only, whilst a game like Crysis, with more CPU utilization could draw more power ?
In the end, if we assume 400w and more, which I think is pretty much doable, 100w a card, 150w for a overclocked q6600, other components, is easily 400w or more. I don't know, you'll probably be running the 620hx near 75% of it's capacity, which I think is a bad thing, and 750w would probably be a better thing, to get near 50-60% of the PSU's capacity.