While it's true that ath and spd are more important than other offense, do not believe that lp and per aren't still important. Teams will still pack it inside if you have no outside shooting. And my #2 all time scorer was a guard with very little per, but a high lp and he could score at will. I have a theory that passing is important for big men in the fb (get the rebound and start the break better), but I haven't done anything in the way of tracking it.
There is no such thing as slowdown fastbreak. If you choose slowdown, the engine will default to normal.
What defense will you be running? I find the fcp to be the best defense for fb, because then ath/spd/stamina that you're so invested in on an offensive end are also of the utmost important on the defensive end.