I would do a 400 Whelen to dupe the 450/400 NE. It does it, and easily with plentiful cases. The headspace issue is not an issue IMO. A light(er) rifle could easily be done.
400gr. bullets (Woodleigh, A-Square, Barnes) we have used will hit 2,250 with RL-15(66-68 grains in Neal's rifle). We have never had any issues and ES is non-existant. I don't think enough RL-15 or VARGET could be crammed in the case to cause issues; bullet pushing enters the fray when doses get greater.
Yes, the WSM should do it easily in 400 or 416 flavor. Feeding must be built around the case. I don't think the WSM case has as much issue with feeding as bore size goes up, but I honestly have not played with them enough and never plan to!
(Just slingin ideas for those out there who may like them).
