Overflow size

[mockranouse]

I'm starting a 29 gallon DT with a 40 gallon sump and trying to decide on an overflow box. I have been looking at the Gl*******s 700 and the nano kits. Will a nano kit be too small for the recommended flow from the DT to the sump? I was thinking that 300 gph would be around the flow that I should have through the sump.