I think I addressed your question from my perspective above, but If I didn't it's perhaps because I think you're putting words in my mouth I haven't said.
My opinion has nothing to do with the guide backing me up. My goal, like last time, is to make a single-shot kill myself, and not to take the shot at all if I think that's unlikely. It's also not a matter, to me, of using a "marginal" caliber rifle (I don't think I used that term) and who is "more willing to risk wounding a animal." It is that, for me, there are certain shots I would not take at all with one gun versus another. It's not that I would always shoot no matter whatever firearm I had and then "risk wounding a animal" no matter what. For example, with a powerful handgun, I probably would not shoot past 50 yds. My friend, who frequents this website is an accomplished handgun hunter, and he can do better. But for me, I would not shoot at a bear with a handgun past 50 yds. If I was handgun hunting, and saw a big bear at 250 yds, I would not start lobbing 360gr .45 caliber bullets at the bear like hopeful mortar rounds (with or without a guide present). I'd pass up the shot (if I could not get closer, or in trying the bear bolted), and probably regret not having my .340.
If I could attempt to hunt brown bear several times a year near where I live, I might take my 7mm if I that's what I had and simply PASS UP some possible shots. But there are some shots with a more-difficult presentation at a certain distance that I might take on a brown bear with my .340 or .375 that I might not take with my 7mm. I would prefer that if I could not easily go back next week or next season without great expense, or perhaps ever.
Similarly, if it were legal here, and I was hunting whitetail deer an hour away, I might bring one of my .223s. I might pass up certain shots on the deer at certain ranges that I would feel more comfortable with my 7mm. No big deal. Pass up the shot, and go back next day, next week, or next season even. But if I had never shot a deer, and was traveling thousands of miles to do so at great expense, and didn't know when I might get to do so again, I would not bring the .223 and possibly have to pass up a shot that might unreasonably "risk wounding a animal." I'd be more likely to bring a 30-06, 7mm, or the like that would give me more, better options, than I would if it was my 50th deer hunt within driving distance from home. If I'm investing a lot of time and money in a hunt, I am more likely to work hard to master, and bring, a rifle that can cover more options. Just my opinion.
And for me (and it's just my perspective), I would feel more jittery aiming a .270 at a big bear than I would aiming at one with my .340 or .375 (which I am comfortable at shooting with much practice). I'm completely comfortable with those, especially in the field, so, for me, it all comes down to trajectory and bullet performance. I wonder if it would be the same with a .416, .454, .460, etc ... I have never tried. Maybe they would make me prone to flinching, even in the field, but it is not so with the 340 or .375.
