I am building a new computer with a Q6600, 2GB DDR2 RAM (will upgrade to 4 when i can afford it!) and twin Radeon 3870 512MBs.
I am a little unsure of what wattage i need in a PSU as all the calculators i found online say different things (onw even said i needed over 1000!). In my New Build thread someone linked me to here (http://ati.amd.com/technology/crossfire/buildyourown2.html) where the Hiper 580, 670 and 730 are listed. I was originally looking at a Hiper 680 (which i figure will work fine as its in between 2 certified ones) but i thought that if a 580 was certified i could get one of those as it will save about £30.
For your system (with Crossfire) I'd recommend 650-750W, especially if you're going to over clock. 580W sounds like you maybe be maxing the PSU out, which will shorten it's lifespan. Just give your self a little overhead as per the wattage I suggested above.
I feel that I should mention Hiper is one tier 4 of the PSU listings (Found here: http://www.tomswiki.com/page/Tiered+PSU+Listings?t=anon ) which generally means they aren't too great. So, if it's in your budget, you may want to consider a PC Power & Cooling Silencer 750 or something along those lines.
Ah, thanks a lot, ill have a look now. If i cant find anything ill go with a 630 or 670 watt hiper as my brother has used one for about a year now and hes had no problems at all. But as you pointed out they are tier 4 ill check out what you suggested!