IME you want the pump to have a grater output then the input of the overflow. You can put a ball valve on the pump to limit the water flow. That way you can adjust the flow to match the over flow. This will help eliminate the chance of breaking a siphon because to much air getting into the u tube due to inadequate flow.
yea, that sounds like a go0d idea to me. Get a pump thats a little to0 big, then plumb a ball valved T off the return line back into the sump to adjust its output?
Ive seen pumps with adjustable flow on them, how reliable are those? Or would it just be better to use the plumbing to regulate it?