Pressure on the block side of the cooling system for sure. If the pump is generating 55gpm worth of pressure (it takes pressure to move a fluid) and the block can support 35 for arguments sake, then there will be unnecessary pressure on the pump. Maybe not on the radiator / coolant lines side of the system, but there will be pressure somewhere.

 

Superado(I believe thats his name) broke his off too.. Stock pump FTW