If you are going to keep a reef then you'd have a real hard time having too much flow. lol
I had 2 750's runningin my 55g and I found it to be adeqaute, but if I had a chance to do it over I would have gone with 2 larger gph
ones. It's also a matter of placement. You can get a sandstorm with the two 800's if not positioned correctly, the same goes for the 1300's. It takes some messing with to get them right so dont get discouraged once you get them.