I think your already set. I would spend more time concentrating on getting into excellent physical condition rather than worrying to much about carrying a firearm thats a pound or so lighter. And of course you may already be in such condition, so therefore toting a 30 mag in either WSM or Wby would not present much of a problem. A 165 grain Barnes XLC BT at 3350 fps out of the Wby will provide all the ranging capability you will need. It will also wack that sheep cleanly dead by yielding 2,500 ft-lbs at 400 yards and 2,200 ft-lbs at 500 yards.
Good luck with the hunt.