M1 is 2000 gph, L1 is 3100 gph. If you're planning to have wave makers, close loop, powerheads , etc the M1 should be more than efficient just for a return pump on a 90 gallon.
I have an M1 on a 90G with a 35G sump. It's plumbed to a manifold running 2 media reactors, a chiller, and just added a Calcium Reactor (currently offline while I replace the recirculating pump). It runs everything and returns to the display with no problem. I run it at 55% 23 hours a day and ramp it up, peaking at 80%, and back down to 55% for an hour a day just to flush everything. I also have 2 MP40QD and an old MP10 (tucked away in a back corner) in the display. That M1 is all you will need unless you are planning on a serious upgrade.