Indeed, a proper Wood Bison bull is about twice the size of what most people visualize them to be. Which is quite the opposite in my experience for most game, usually you go in expecting it to be bigger and experience a bit of a let down seeing them at your feet. I've spent a few years around Wood Bison now, my first encounter with them was on the way to Yellowknife, and I didn't see them for a few years after that except sporadically and at a distance and went to Africa. Took a heavy Cape Buffalo, and then returned to living and and working in Bison territory and even having seen them previously, was taken aback when I encountered a Wood Bison bull up close post-Africa. He was so much bigger and heavier than the Cape Buffalo I'd hunted it had me stopping and gawking like a tourist.
Now I've become very familiar with them again, and see them more days of the month than not given my job. They still look big every time I see them and frankly, .30-06 is doing them a disservice, they're an honest .375 class creature even if harvested successfully with lighter equipment. When things don't go perfectly they can show how unbelievably tough they are. I've hunted them in Alberta and quite frankly it seems like they make up their mind on the spot whether to give up, or be tough, and if they decide to be tough few things can take more of a beating on this planet, and none in North America. If one is setting out on a purpose built Bison hunt, such as for the control herd, pack a .338 Mag if you want to avoid equipment with less overall use in North America like a .375 or .458. At the bare minimum a .300 Win Mag and 200gr+.