once you go to a strker your going to need the +4, but keep in mind your going to need alot more then just the longer swinger, your going to need a better clutch, youll need to revalve your shock for the longer swinger, youll have to port your motor for the stroker. If you plan on getting a 4mil later wait and do your porting then.
for what your running now a stock length is fine. once you start modding then owrry about going longer.