Are you using an Apex?
If so, look for an Apex-ready pump (or even better, the Neptune Systems COR-20) - the additional data and diagnostics you get is well worth the investment.
Think about it ... the return pump is the heartbeat of your entire system ... if it fails, stuff dies. So being able to get real-time data on how well the pump is running and detect emerging faults is a good investment.
Also, I'd highly recommend not using a single pump, but using TWO pumps running in parallel to give you more safety.