I've been researching this one myself. I can't give you any advice based on my experience, but I can impart what I've found - keep in mind I don't know how reliable this info is. It seems to be a general consensus that several small power heads are better than one big one. I also read an article that said you should have water flow 30 times the volume of you tank with FOWLR
and 50 times if you have a reef tank with demanding coral. So in your case two 750 gal
/hr power heads should be good - if not overkill. I'm shooting for 35-40 since I have no plan to keep demanding coral, as I don't have the expertise to keep them alive anyway.