If it is top speed you are looking at, typically the higher number of ports leads to higher RPM's a motor can produce. For example a 7 port normally will have higher RPM's than a 3 port from the same manufacturer.
Also, gearing and the proper pipe makes all the difference in the world.
But, my opinion, top speed is grossly overated, as having a motor which is good for the other 95% of the track is what matters.