With that being said, I am going to be using a reeflo Dart pump (3800gph) as a return pump and a Reeflo Hammerhead (5800gph) on my closed loop system for my 240 gallon sps dominated reef tank. Some people say that I am a little on the low side.
For a 265 gallon, I would suggest at least a reeflo dart for the return pump and at least another reeflo dart for the closed loop system. Personally, I would actually go a little higher then that, even for a fish only tank.