On almost any engine, any load you can take off the engine will translate into more usable power. An electric water pump is not always the best option for a daily driven street vehicle, but could free up 10-15 hp. You should consult with a reputable water pump manufacturer like Meziere.

Well most electric water pumps only flow around 35gph which is not enough to support a street car. Meziere has one that is 55gph that would work. I would just get a high flow belt driven one and add the electric fan that will work better than a stock one and provide much better cooling and in return give you more power.

You might be just better off with electric fan and under drive pulleys. I am not a huge fan of the electric pumps. Expensive for one thing, but have had people have mixed results with them, some very good some not so good. A few experts have mentioned that flow alone is not all required, its pressure as well which most of the pumps could never produce what a belt driven pump does. Also the electric pump draw around 10 amps (or around 140 watts of juce) and long term reliability might also be an issue. The regular waterpump is a dumb simple device, and when all said and done you won't save that much gas by going electric. Likely save more by checking your tires for proper inflation ;)