Has anyone seen any info on this, like .375 and up?

Check out shortmags.org
I think there've been 375, 416 and 458 iterations of the WSM case, with fairly expectable results.

John Lazzeroni has necked up his short 30-caliber Patriot to both 375-cal and 416-cal, He call the 375 the Hellcat and the 416 the Maverick. I have a Hellcat with a 23" barrel and can get 2600fps with the 300gr Nosler and still maintain sub-moa accuracy but the recoil in my fairly light rife is stiff. Much more comfortable to shoot around 2525 to 2550fps.

His website shows somewhere around 2400fps with a 400gr bullet for the Maverick which mucst be a real handful to shoot.

I would expect the WSM case necked up to produced velocities somewhat less than these ...maybe 100fps less.