IMO save yourself the hassle of having to deal with microstutter. A lot of people notice this from SLI/xfire and its annoying as hell. But if you do decide to get sli:
edit: just saw you're going triple monitor, SLI makes a lot of sense in that case. Be aware that the grass may not be greener on the other side, triple monitor has issues for
both AMD and nvidia, period. Some games will not work.
If you're overclocking the CPU or GPU substantially, you'll need a better PSU. OC'ing can add a *ton* of power draw, 200W or more. If you're oc'ing both gpu/cpu then i'd say 850 miniumum, 1k preferred. I'll try to dig up the review, but one 580 sli review mentioned nearly 900w power draw from the wall - with both gpu's heavily oc'ed. OC'ing is no joke when it comes to power draw. What works at stock doesn't when oc'ing.
Anyway, as far as specific recommendations it doesnt' get much better than the MSI lightning or Gigabyte super OC if you want to overclock. Go to overclock.net - they have a huge database of successful and verified 580 / 570 overclocks and the MSI lightning with twin frozr 3 is consistently , hands down the best. If you don't care too much about oc'ing, EVGA is a good choice - most of their models use ref cooling, but are fantastic for SLI. EVGA also has the best warranty in the biz.