Kevin,
While identical in two dimensions, the .30-30 and .375 are substantially different in head thickness. If you have an example of each, please section them and it will be readily apparent to the naked eye that the .375 is much thicker. It is a much stronger cartridge and can handle 52,000 cup. The .30-30 case cannot, nor should be loaded to anything that even approaches that value. My concern with hot loading the .30 WCF is primer pocket blow-by and quite possibly head separations when loaded with Paco Kelly-type loads.
As James alluded to, comparing their strengths is comparing apples to oranges.
Moose,
Thanks for your last message. Your point is well founded regarding the ease of opening an action and high pressures. When the strain makes your eyeballs sweat, you know you've gone too far. Your hunting experiences are also appreciated. I wish I had tried this bullet in my old 94 Trapper before trading it, as I would probably still have it. As it stands I'm leaning towards a Marlin Cowboy, although you never know what gems may appear on the used market when the time to buy comes along.