What Size Should My Overflow Plumbing Be?

[Palster]

I am currently building a sump for my 135 FOWLR and I got to thinking about the size of the plumbing I will need for the overflow drains from the tank. I was wondering what size of PVC pipe and bulkheads to use (I haven't got the tank drilled yet). The return pump will be a Mag 12 with 1" pipe returning to the tank and according to Reef Central's Head Loss Calculator by the time I take into account all the plumbing and head loss I can expect some where in the range of 850 GPH. I was thinking I should plan my plumbing to handle up to 1000 GPH. My question is with a design flow of 1000 GPH should I be looking at using two 1" drain lines and bulkheads or should I make these drain lines and bulkheads 1 1/2" or possibly a single 1 1/2" drain? I was under the impression that 1" PVC will handle approx. 600 GPH and 1 1/2" PVC will handle approx. 1300 GPH. I was just curious as to what size the plumbing is on a typical 135 gallon tank? My current 90 gallon has a single overflow with 1 1/2" plumbing draining into the sump (it was plumbed this way when I bought it).