I think you did swell. You covered all the bases in regards to need and now you are free to just go after want.

Their are a number of British Rifles in 9.3x74R that have been rechambered from the 400/360. If you could find one of them for a reasonable amount you would be doing fine.

I think I see a hole in your arsenal at the 400 level and as you say at the 577 and larger level.

I have a 375 in a pre 64 Alaskan and think heaps of it.

Good luck and keep us informed.