how does it compare to jt and elefant
The JT and Elefant kill medium tanks in about 18s (but 8,8s with a single faust thrown in) from the first shot and kill a 1040hp heavy in 26,4s from the first shot. They have pretty much double the AT DPM compared to the ISU-152, although this advantage does get neutered against 640hp vehicles because of the overkill damage that's required.
SU-85 is probably superior to Elephant vs mediums probably vs Tiger also.
The SU-85 needs about 45s to kill a Tiger I. The Elefant needs 26,4s to kill an IS-2.
At vet 3 the SU-85 needs about 27,4s while the Elefant needs 15s.
The Elefant has far superior DPM, although it mostly loses the advantage against 640hp vehicles because it needs to deal significant overkill damage and needs a third shot to deal the last 40 damage. But as I've said, in case both are supported by infantry who can deal even a single snare worth of damage, the Elefant can kill even medium vehicles almost twice as fast.