Main Difference are
1. For unicast packets, StackWise Plus supports destination striping, unlike StackWise support of source stripping
2. StackWise Plus can locally switch. StackWise cannot. Furthermore, in StackWise, since there is no local switching and since there is source stripping, even locally destined packets must traverse the entire stack ring.
the limit of 4 switches in a stack your referring to is StackPower and not
StackWise Plus. Stackwise Plus, like Stackwise supports up to 9 switches in a stack
nice document on the same
Hope it helps further