Beside a power consumption increase, operating a centrifugal pump at high flows, in xs of the design point or the BEP, may lead to what is called the "run-out" point where the NPSH available becomes insufficient and the pump may suffer cavitation damage. Suggest you move this query to the "pump engineering" forum where no doubt you'd get plenty of useful advice.
Risks include: not having enough bhp (that is one reason why centri. pumps are started up with discharge valve nearly closed), not having enuff margin between NPSHA and NPSHR, vibration due to suction (sometimes discharge) recirculation; and, seal pressure problems.
