So the extra screens aren't useful. Begs the question of why go through the expense and hassle of setting it up then. Hopefully it's more useful in other ways (day trading, racing simulators, etc.)
Don't you guys just use the extreme PSU calculator?
http://extreme.outervision.com/psucalculatorlite.jsp
Btw, I also have the GTX480 and I'm using a 700W supply and have had no problems thus far. All my games are running just fine :)