Overflow question

[chrisd]

I am going to be switching over to a sump for my 54 gallon corner bowfront and because my tank is not drilled and is made of tempered glass I'm going have to invest in an external overflow. I've been doing some research and it appears that the Lifereef overflows seem to be the preferred brand to go with. I'm going to have Bow Valley Aquarium build me a 18gallon sump and was looking at getting a Rio20H which would give a flow rate of around 990gph at 4ft head. My question is would a dual overflow with a flow of 1400gph be too big for this setup? The single overflow only has a flow rate of 700gph. I've read in certain areas that the overflow will match your pump output but I'm not real clear on if that is true or not. Any advice would be greatly appreciated. Thanks.

Chris