Depending on the pump line, you could end up with a larger pump even though it has a smaller label HP. For example, the 1/2 HP full rate Whisperflo is actually a larger pump than the 3/4 HP up rated Superpump. In fact, it is bigger than the 1 HP up rated Superpump as well. When choosing a pump, it is important to look beyond the label HP and see how the head curve compares with your current pump's head curve.

I would agree with Carl that a motor swap might be both cheaper and easier.