Apart from F-class, I also compete in Big Game Rifle Club comp, rules state 375 is minimum, MUST HAVE 5,000ft/lbs at muzzle to qualify, big bore starts at 45 cal, but we changed the rules to accommodate smaller calibres.
A 6mm doesn't even come into the picture, and yes, I shoot prone, off-hand, from a bi-pod and even prone from my truck or standing in the tray…anything else you want to know.
You can quote physics all you like, experience trumps physics in regard to recoil, the bigger the recoil you are accustomed to, like 500 Nitro, 505 Gibbs or 600OK make most magnums, including the 375 Weatherby, feel like your 6mm…
Cheers.