Sverre: No to the fmjs and no to 200 gns. I would feel confident with a 240-300 gn cast swc, over any good formula using Unique, 2400, or H110/296 powders, leaving your barrel at 11-1200'/sec for game up to and beyond 300 lbs.
Your concerns about penetration with a 200 gn bullet in 43 bore may well be justified.
Hard enough isn't the issue, you are correct. It is the ratio of length to bore diameter that helps determine a bullets ability to penetrate. Long and narrow penetrate better than short and fat, I feel.
I don't think you're wrong at all. This is exactly how lots and lots of guys, me included determine which caliber, bullet and load, rifle, pistol or shotgun we want to use for the specific hunting effort in which we are to be involved.
Have a go at it and let us know what you come up with. Mikey.