I was just curious as to you saying you prefer a 300 and 340 Roy, as to what size game and range. My longest deer kill was using a 6BR at 400 yds, LRF.....made it all of 25 yds or so after the hit. I too have enjoyed doing alot of R&D as many Loony's here, but getting narrowed down to keeping it simple and what works, minimizing blast to ears and recoil, so I have focused mostly on everything from 221 to 7/08, a 338/06 and 350 RM for good measure, but those are long gone, and the old Swede. I was a 6.5-308 user pre-260 Saami, after having Swedes, later 260s, and a Creedmoor, I did like it fine. It worked well like others, but to simplify cartridges I load for, I weeded out all but a 47 Lapua for now. I could flip a coin between it and the CM based on my experience.
Nothing it will do that another good 6.5 won't, but the 47 is very pleasant and a tackdriver. The 9.3 was on my bucket list, but time is short, so not sure if I will get around to playing with one, but it would be a top choice if I planned an Elk hunt, or even Africa. I like Mid-bores for a purpose, and never felt I needed to reach beyond the distances you do. But found the 6s and 6.5s to be very enjoyable. The 6BR has been one of my most enjoyable, having had many built. I guess I never needed a large 30 or 338, though owned a 338 WM for a short time. Shot a 416 RM once, never again. Hate recoil, and blast, already have a touch of tinnitus at times, likely due to shooting without proper protection when a youngster. None the less, we all like a different flavor I suppose. I do notice many over the years, "down-sizing" or Right-sizing, whichever they might call it, to rounds more shootable, and they continue to fill the freezer. I'll admit to still owning a 243, flat, accurate, deadly, mild. Just never warmed up to 300s and 340s, but respect what they can do, and owners who shoot them well. That 375-08 does sound interesting, only b/c back in the mid 90s I mocked up a 338/08, though know it was wildcatted years before. I suppose you can ring out a 300 Roy over those open areas. I guess in the end, we all use what works for us, based on experience....and after my first rifle, a 7RM, 30 years ago, I have gone the opposite direction of many. I guess you could say I am in the "Less is more" crowd.
