>>64403784
>Would various Panthers II and E-75s have been able to stand up to T-54/55s, Pattons, and other classic equipment?

The 88 is a good gun, but something bigger would be desirable to ensure penetration and kills at various angles and places on the tank. T55's and M47's would have armor dangerously close to blocking an 88 shell at reasonable engagement distances (though the M47 does have a quite vulnerable turret), this is bad.

If they were to be considered 'equal' on the battlefield their armor is already there for the most part (though I would compare a Panther 2 to late model T34's, instead of something like a T-55 or even T-44, it lacks the protection to be an equal of later tanks), but the gun definitely needs to be upgraded. The 128mm is just too big to practically fulfill the needs of an MBT, and while it would have no problem with any tank besides shit like the T-10. A 105 would probably be the closest thing, as the germans already used 105mm guns (albeit not generally as AT guns), so it is likely this would be the calibre chosen.

>What about the older Panthers I and Tigers II?

They would fall flat for the most part. These are both wartime vehicles, for a losing and desperate side at that, so they lack much of the quality and refinement of later vehicles. Against their familiar and intended foes they would be fine, but anything above an M46 would really be pushing your luck. It would probably be a turkey shoot for the enemy regardless.