Don't no if this will help but it may Little Giant 4mdq-sc is rate I think around 900 gph and is 1" in and 1/2" out. It iwll run your manifold no problem. Hope it helps.
I just got bad news. On the reefcentral's overflow calculator I just found out that for the projected 1000gph flow I would need a 1.5'' drain. Unfortunately I have a 1'' drain with a 1.25 durso stand pipe on top, so it will probably not do :-(
By the same calculator I'll probably have to go to 650-700gph (I don't know wheather with the durso pipe or not. That's a bummer.
One more stupid question: how do you get those *huge* sumps under your tanks? You take the tank off the stand, then put the sump, then the tank? Because through the tiny doors of my 90gal I can fit at a maximum 2 x 15 galons tanks (not a 30, 2x15 g). Any other way?
I DIY my stands, so I can remove the middle post to put the sump in. Some people do the method you mentioned above, with the tank out of the way, put in the sump, then the tank. A few of us learn the hard way after the tank was in place and filled with water, rock and sand that the skimmer is too tall to get into the sump I am sure some others can give more examples of the sump-in-stand blunders.