Maximum mass on 8E thrusters (unengineered) is 3360T, maximum on 8D+G5 DD is 3308T [1], so a ship which is heavier than those points in conventional configurations seems unlikely.
Set aside at least 700t for core internals of a similar size to the Cutter and a bit of extra weight for utility slots and assume the Panther's hull mass is about the same as its cargo capacity to match the various Type-N freighters and other bulk haulage designs, and that sets a maximum of about 1300t cargo capacity before it can't actually leave the dock in some reasonably normal setups.
[1] Admittedly if you're D-rating the thrusters on a Panther Clipper to "save weight" you may be working against the ship's intent, but I'm sure people will do it anyway.