most of the ehiems have the most gph for canistors you might want to consider dual canistors i ran a eheim wet dry canistor sorry forget model # and a eheim pro two that would handle the load of your tank.
heres a link thats shows you how to build a sump system http://www.cichlid-forum.com/articles/diy_sumps.php
also search the site here theres so many ways to do a cheap sump/wet dry system and will be much better for the size of tank you have in mind
Eheims actually run a lower gph than most other canisters, but their pumps are much stronger, and will not get clogged very easily. For a 265 I'd start looking at the eheim 2262, and I'm sure Harley will add on to that. For this tank I would honestly look at setting up either 2 big canisters, or one nice wetdry.
Thats alot of money. I hope Large cichlids knows what kinda investment maintaining a 200+ gallon tank really is. This is exactly why I'll be happy with my 90-100 gallon tank in a few months. Because I know I could prob get by with just my two Emporer 400's if need be.
Still if money isn't a priority, those Eheims are some of the best.