Well, over at Chadron Fur Trade Days (the only place I can recall ever doing woods walks) I'd continue to go with my .45, but nothing less... (the reason) Some folks used .32's, .36's, and .40 caliber rifles - and they couldn't topple some of the heavier metal animal silhouettes with those smaller calibers, and to be honest - I aimed high on the metal to topple the ones I shot at with my .45...
So, it depends on (IMHO) on what will be required to be done during a woods walk / and usually you're not going to know if you have enough rifle or not, until you're doing the woods walk...
Ideally, IMHO - a .50 caliber would no doubt serve you the best as a minimum caliber, but the .54 is probably the one to bank on.
Just my opinion...