How much recoil is too much?

[Canuck44]

I went out plinking yesterday and am nursing a sore shoulder today. I went through a quite a few rounds with the 270 which should be ok but I think the real kicker was my 45/70 guide gun that I was shooting 350 grainers at about 2100 fps+/-. This load seems to be ok for accuracy (2" or less at 100yrds) and I am planning on using it for moose, elk and bear. The recoil this is supposed to put out is in the 35-40 lbs range which is about double the 270/30-06 level.

I can shoot it OK and don't mind having a sore shoulder once in a while after test sessions of 25-30 shots but I have heard of people getting injured by big calibres that put out 50-60lbs recoil and am wondering if there is any chance of getting anything more than discomfort from this sort of shooting. Maybe I should get one of those shoulder recoil pads? What do you guys use and how much is too much?