I am selling my xr100r and getting another dirt bike. I am having a tough time deciding which one to get. crf450r vs. yz450f vs. kx450f vs. 450sx-f vs. RM-Z450. I think some of these bikes only have 4 gears? Which is better 4 or 5 gears? Which bike is better? Why is one bike better than another? BTW, I will be riding on gravel/dirt roads, fields, some tracks.