The Ultra Mag seems like a lot of gun, especially as for the vast majprity of people, the recoil will be too much to shoot it well enough anyways. To each his own though, if that rifle really does it for you, you will not be under-gunned.
I used to be into the big heavy calibres too until recently. I got to thinking about the areas that I usually hunt and came to the realization that there isn't a whole lot of opportunity to shoot at anything all that far away. Areas are all getting grown up, the new cut-overs aren't the big open clear cuts like they used to be. Most of the time the longest shot you could make is only 300 yards or so. Plenty of lighter cartridges and lighter rifles that can do that job well enough. Light, easy to carry rifles are a god send after a weeks worth of hard hunting. The other thing I'm getting rid of is big bulky scopes! Once again, used to think the more magnification the better, well with everything getting grown up and the brush so tight, a good set of peep sights has become much more prevalent in my arsenal.
I grew up in Northwestern Ontario and most people used the standard 303 Brit, 308 Win, 30-06 Springfield, 300 Win Mag with great success.
Good luck in your search!