Hi nitro neil, mugenb46 will be able to give you all the details regarding those two motors, but basically the 3 port sport is just that, a sports motor for general use. The 3 port R Spec is a true racing motor. The porting on the R Spec will be completely different as will the crank I would say.
If you are going to be racing a .21 in a buggy, go for the 3 port R or the 7 port. In a truggy go for the .21 5 port (it is a beast down low) or the .25 6 port. All of these motors run awsome with the Dynamite 086 pipe with the exception of the 7 port which likes the Dynamite 053 pipe. I am running the 7 port with 053 pipe in my buggy and it is an excellent combination.
There is also a new Go 0801 pipe on the market which sounds like it might be the goods. Which ever Go-Tech engine you buy you will be happy. These engines offer great performance and superb value for money