how would it differ from the current tank destroyer in terms of ability though?
It would be armed with a bigger gun. It would probably still have the weaknesses of the SU85 but it could put some hurt on the Panther and Tiger, which the SU85 can barely scratch.
It would probably be a late game unit. There would be a fine line to balance though, since in combination with an ISU152, it could be very OP, but then again there's the KT plus JGDTIGER combo....