No, you don't need a 1100W. The 550W minimum power requirement is for the entire system with one card. For SLI power requirements take that system power requirement and add the maximum graphics card power for the second card and you get a figure around 775W.
I would have to say that you may be able to get away with a 750W PSU, but it could be close. An 800W-850W would give you a greater margin of safety.
Really? I got the OCZ one as a reccomendation that OCZ made really great PSU's. I will go ahead and look into a 800+ PSU, but i'll try the SLI for now with 2 cards to see if it glitches any. If i have problems i'll pop one out and wait for the new PSU.
You might be able to get away with a 750w PSU of amazing quality, but probably not with OCZ, only a couple of their lines of PSU were good, and the rest were junky, so without knowing what exact line of PSU you have I can't recommend anything either way.
OCZ is pretty high end, yes, they did have some bad times, but they have really cleaned up. I would say go 800+, but who knows, OCZ is pretty high end and does normally give you what they tell you they will, if it is a newer version. My OCZ PSU is great. The first series such as, STealthXstream, ModXstream, etc. were not good, but now they say for example StealthXstream 2 which is normally pretty good.
Look on the back of your PSU and there should be any area were it tells you the power of the 12v rails, under that it should tell you how much the 12v rails will supply. My 600w supplies 580w off the 12v rails, which is pretty good. Yours should probably be something around 700~730w on the 12v rails.