Within reason higher flow rate is usually desired. This raises fluid velocity and thus the convective heat transfer coefficient which is the primary heat rejection process here. But 50 gpm is quite a jump from 20 gpm, the possible issue being there is not enough time for the air to convect the heat out of the core.

Although I don't know the life or maintenance specifics on any of these I would tend to shy away from them because they are not brushless. My preferred pump would have permanent magnets and a built in inverter thus no brushes or commutators to wear out. And it would likely cost more.

Kitz