Random thoughts
The 35 Whelen is not enough...really? It is considered just a baby step below a magnum, big enough for large bears. If you want more punch than that, then you are truly need a very large case. You have to be careful about case diameter and breech pressure. The larger the diameter, the more pressure effects the breech face. When you get so big, the pressure needs to drop to be safe. There are diminishing returns , I would think for going too big. Of course the 45-120 is a big case and people have loaded them up to pretty high pressures...higher than I would like. I know that magnum cases have been experimented with in the Handi rifle and for the most part have had disappointing (failures) results. Putting the 35-120 with enough pressure to out do a 30-06 case may get over your breech face pressure limit. This is all speculation on my part, I have no real experience with large high pressure cases. I just know that the 30-06 is high pressure and the Handi handles it well. I was under the impression, that it was at the upper end of what the Handi would handle.
When Quick sees this he will have a comment, I am sure. He has done a lot of experimenting (first hand experience) with the bigger cases and what it takes to be safe.
Good Luck and Good Shooting