I hear ya 100%, my only shotgun gauge is now 12 as well and I’m going there, .308 and 12ga, plus rimfire. I do debate if a painful program to convert everything to .257 Roberts has any merit. But I know it doesn’t… that other era’s call is strong, and I just plain like shooting .257 so much. Feels like forgetting a gal once and for all that was pretty great.
257 bob sure does have merit, I got down to one bore and one cartridge that I can feed factory if I stock up (which I have). I don't reload but have been saving all the brass, have a good bucket full so far, maybe I'll grab some components in near future as well just in case retirement brings me time to take up the new challenge and develop a load. If you boil your list down even further, add in barrel life requirements, recoil (watch in scope), and maybe a couple other categories, truly minimize (or maximize efficiency) you might get to the bob? I had a bit of a struggle giving up the 270 win but was adamant that I'd be into 21st century developed cartridge for max efficiency factory (reload optional). You can shoot same amount of powder as 30-30 but 21st century 6.5mm 123gr bullet triples effective range on game and will plink all day to 800 if that's long enough for you and pretty sure you won't be able to wear the barrel out, and a case that's surely to be available a long time (7.62x39). You're still attached. So the only angle you haven't really debated is any of the 21st century options for possible fit as in time their ammo's will be far more frequent on shelves and eventually few of the 20th cartridges will be. Sort of future proofing for my kids.