I carry all the time, and it is almost always either a 5" 1911 .45 or my Ruger Security Six 4" .357 as the main gun with a Ruger Sp-101 as back up. It all conceals very well, and the Security Six is almost exactly the same size as the GP-100. So concealment should not be a problem in most circumstances. As to hunting, as has been said, a 4" .357 may not be the best choice, and I prefer to hunt with my 7.5" Blackhawk .45, BUT my last deer was taken with that Security Six. 158gr cast bullet at 45yds head on, and the buck took three steps before falling over dead, and not a twitch. So I dont feel undergunned in the least for our small deer down here, and dont think you will have any trouble with a double duty handgun as long as you can place the shot where it needs to go.
Now having said that, assuming money allowed, I would personally probably use the fact that a compromise gun isnt really the best hunting gun as an excuse to get two guns. And did get a GP-100 6" recently also, but haven't had a chance to hunt with it yet. Whatever you choose, best of luck.