Never taken one over the top, so I don't know. The aft bilge pump is a Rule item that pumps 800 gallons/3000 litres per hour, and the forward pump would probably kick in too if it was really bad, but again, I'm unlikely to ever be out in risky conditions.
I'll look into how easy (or difficult) it might be to get scuppers fitted through a twin skinned hull, but it's a low priority.