survivability It would be nice to survive the occasional PAK40 round in a Jumbo! I would have to simply deal with the underpowered issue. Of course I would switch the 75mm gun for a 76mm at the first opportunity.......
Why not? It's only real issue was firepower, which the 3rd Army fixed by retrofitting the tanks with 76mm guns as soon as they arrived.
Most American flamethrower devices came as kits that could be fitted to any M4 tank in the field as operations required. Thus it is well possible that there may have been Jumbo Shermans with flamethrowers added.
The French 105 mm armed Sherman. Takes out T-55s with no problem. Opps, not WW II. I'll take the Firefly. Lest they be temporarily blinded, I read how the crew had to close their eyes before it shoot.