As long as the GPH rating on the overflow is higher than that of the pump, you should be okay. Just be certain to adjust the normal max water level in your sump to accomodate for a power failure. I run an HOB overflow and have never had a problem with the sump overflowing.
You can also raise the return hose a bit and drill a vacuum release hole a bit higher than the existing hole (still under normal water line) in the return pipe so less water flows back into the sump after a power failure.
No problem with the fish bumping it, they really leave it alone. They do like to mess with pump that removes the air from the overflow, but it has never lost flow.