Well don't overlook the Encore. Rimfire to belted magnum, barrel changes don't require any tools beyond a punch, decently accurate, pretty light, and if you're throwing a tax stamp on you can also get wierd with it.
I have an Encore pistol with a brace and an SBR'd contender and they're among the most packable rifles in my safe. With a quick detach muzzle device on your can and a folding stock, you're looking at a rifle that tucks inside most rucks or can carry on a sling all day.
The 8.6 Creedmoor is on the way, if you're interested. Less guesswork than the .338 Federal. Over on silencertalk iw as following the .338 federal subsonic loads (250gr from a 1:7 twist barrel) but folks were talking about needing magnum primers in the brass, opening flash holes, and still fighting powders. The 8,6 whenever it runs out is looking at a faster twist, and with the cartridge design should be less issued with inconsistent ignition.
The other thing to look at would be some of the dedicated subsonic cartridges, your Whispers and the .338 Spectre. If you're comfortable outside the 30-.338 range you can go with one of the oldest subsonic thumpers in the market, a fast-twist 45-70.