Be Quiet! only has one 900W PSU as far as I know, the Dark Power Pro 900W.
-- is this yours?
If so, it's a mediocre unit made by FSP - http://www.pc-max.de/artikel/netztei...ro-p8-900-watt
Ripple suppression is pretty mediocre, extremely close to ATX spec on the +3.3V and +5V rails at 50% load, and exceeding ATX spec at 80% load. Not impressive. +12V ripple is not great either but within acceptable limits. Voltage regulation is good, and it will deliver the power its rated for. But the high ripple is kind of a big deal. Will it power two 580s? Yes. But it may cause some of your components to malfunction sooner than they normally would have.