lipo and 9xl

[squeeforever]

i have finally decided i am going to get the 9xl to run in my brushless revo to race. mainly for longer runtimes and i dont need to do 70 mph on the back straight. i found some polyquest 3s 4000mah lipo packs and am wondering what kind of runtime i should expect under normal race conditions. also, whats a good charger that i could charge and balance 6s lipo on? i was thinking the mrc rb989 superbrain.

EDIT: the packs are only rated for 64 amps max. will these be ok?