It all depends on how well built each unit is. You can make a STOUT 8.8 if you use the right parts. To specifically answer your question yes people have used a 9" instead of 8.8 but I can't seem to find the threads right now.
the 8.8 is a strong rearend. they got people running 8s with them and with 4 lugs.like gary rohe was couple of years back.
you got to make sure you dont use all the stock hardware in it.
like 31 or 35 spline axles and locker unit , and you can get the ford 9 in ends added to it also. if are going to be running low 8s or 7s go 9in.