My pump is 158GPH and it goes through three very complex waterblocks, a tight radiator, and about 7 feet of hosing. Theoretically the more GPH your pump can handle the cooler the thing will be because more water is flowing over it at the same amount of time, however I feel that GPH is a zero sum game because then the water is running through the radiator just as quickly and thus not cooling itself down as quickly. I use an Eheim pump, it's designed for aquariums. Any pump that says it's "designed to water cool computers" is overpriced.
That pump you linked to looks like a pretty nice one. It's got the rubber suction cups so that it won't be noisey against the case, and it's looks pretty small. However, I'd suggest a Hydor pump, because they use ceramic shafts, which means very little heat is transfered from the moving components of the pump into the water itself. Plus it only uses 11Watts so you could even splice it right into your computer's power supply... or get one of those harnesses designed for the job.
http://www.dangerden.com/mall/Pumps/Pump_hydor.asp