whats better 6a or 6al

but what is the max rpm for the 6A?

had an input shaft brake in my transmission a few years back it broke when shifting from 2nd to 3rd at fullthrotle and 7500rpm my tach showed over 8000rpm before i got of the throtle so you will probably blow the motor long before the box gives up... for me, i will buy a box with a limiter in it as soon as i can make up my mind what kind of box i want