I'm pretty set on the Syncra Silent Pump and may go with the 3.0 because I was using the
http://www.reefcentral.com/index.php/head-loss-calculator
and the 3.0 is 714gph Total losses are 5.19 feet of head pressure, or 2.24 PSI. with a flow rate of 417 GPH used a mag7 for comparison. added the +14 to come out with 431.
the 2.0 used a mag 5 + added the 68 since mag 5 is only 500gph and came up with 371gph.
I'm guessing these are rough estimates. Now if you go with a 1" return it would give you less head loss and more gph.
Comparision : Mag5 with 1" return +68 =
Total losses are 3.49 feet of head pressure, or 1.51 PSI. with a flow rate of 406 GPH
Comparision : Mag 7 +14gph
Total losses are 3.97 feet of head pressure, or 1.72 PSI. with a flow rate of 495 GPH
So I think you called it right with the Syncra Silent 2.0 Pump as that would be in the 7-10X per hour flow through the sump. This is just however on just 40 gallons and not counting the sump volume of water in the total. If I'm thinking correctly. Everything I have been reading is Syncra usually underrates their flow. It seems it really comes down to the plumbing and how many elbows etc. I'm working up a drawing in paint..lol