For my style of driving and the type of tracks I usually run on I go for the 5 port for it's better bottom. The 7 port has it's powerband more on the higher side, so for most tracks with short run ups to jumps, you won't be hitting the peak of the powerband often. On euro style tracks that seem to be more long-flowing, the 7 port would have an advantage. 5 port is more forgiving too as you'll be able to hit the peak sooner. Also, the weight and gearing of your buggy is also important. For example, Losi 8's weigh quite a bit less than my Mugen MBX5R and they seem to run better with a softer bottom motor with stronger top as high-torque motors tend to upset their lighter chassis.