There are a couple of differences. First the WFE series use more efficient motors than the WF series, about 12% more efficient. Second, the WFE-3 is a full rated 3/4 HP pump while the WF-23 is an uprated 3/4 HP pump (1/2 HP full rated equivalent) so they aren't really the same pump. The WFE-3 is really the same pump as the WFE-24 and the WF-23 is the same as the WF-2.
Also, upsizing the motor doesn't change the pump. The pump head curve is determined by the impeller not by the motor. The motor is simply appropriately sized to the impeller so it doesn't over heat and fail prematurely.