An AVRE uses a 290mm Mortar. Essentially just lobbing a bucket of HESH at something.
The Sturmpanzer IV is actually equipped with an assault gun at 150mm.
If anything it should be doing less damage and firing more often.
If we want to talk bigger we need the Sturmtiger(and I want it!) with a 380mm rocket launcher. and a rear mounted Grenade launcher. That'd be some epic shit.
you're right i totally got the two confused! so what i was suggesting here was the sturmtiger in the OP.
so the SIV should be P4 armor, options for skirt upgrade and MG with a long reload or a very short cooldown that fires a shell bigger than a stuh?