Reef centeral has a nice calculator off the main page to give you a very good idea on what to expect from any of about 100 possible pumps.
Some of the kep things to consider is how high you will pumping this water, and how fast do you want to pump it. If your just doing this for water changes then your probab ly only pumping 5 to 30 gallons at one time (dependent upon the total sysyem volumn), so is it important for you to get it changed out in 3 minutes or an hour?
Personaly I'm looking at a 1,800 gph mag drive pump to pump from my basment sump up to my tank roughly 12 feet above the sump. Since I'll be having the sump, skimmer, and refudium in the basement heat build up from the pump is not a factor for me, as it will decrease the use of heaters for me rather than increase my need for cooling.
Dennis