i run a 450 dirt bike with lots of mods for hill climbing and it had a stock swing arm and id smoke alot of ppl casue i had alot better body english than them. they sit neutral with flat back, imup over the bars throwing the bike around. and if you go to long then all the power is going to do is spin the tires due to low weight on them when you go longer swing arm. and ya the guy who said 6-8in would be good is proly right, your only +4mill and alky, its got to be runnin around 100horse but you souldent go to long either, id call someone at LSR or someplace and get a better idea mabe?