If it's a full siphon it will pull a lot more too.
http://www.beananimal.com/articles/h...-aquarist.aspx
I know my 1.5" can't be maxed out by my laguna 4200 pond pump. After head-loss I'm sure I'm getting more than 3000 gph into the display (I do have it throttled back however I ran it full bore while I was curing/flushing crap off my rock)