motors????

i have been reading around a lot of these forums about different motors.

im looking to get a motor for my erevo that im building but i cant figure out witch motor to go with.

i heard that you just take 35000 and divided that by the amount of volts your going to use and that well give you the kv you want.

so id id that i got 2400 and thas like a 7xl motor. but then also some one on this forums said it would be better to go with a 9xl motor with 4 cells cause it would run better.

im confused lol.

all i want to do is go fast and just have fun. to track racing or anything. but i dont want it to overheat too.

so should i go with the 7xl or a 9xl. or a 8xl. and witch one? thanks.