In my opinion, it's not the smartest move to overclock a $500 gpu for an extra 3 fps. And for the record, we get it. You have a GTX 580. You're awesome. You don't need to keep bragging in every thread.
Those #'s are on par w/a good oc on air for this card. You'll have to post up fps when the new pack comes out. Dunno if you're on air or water but if ur watercooled I'd bump up voltage tentatively and continue to go north on your clocks. I haven't seen many 580's stay at 900+ for anything other than benching so you're pretty much "there"....
Oh yea afterburner does work with all but I think you need to get the beta version to have an unlocked voltage slider. Search for something like "voltage wont unlock on afterburner" and it'll redirect you to an ocn thread telling you what you need to dl (i think it ends up being on guru3d).....