If you can handle the .375 without a flinch and shoot it as well as a much smaller rifle then perhaps you should consider a .30 caliber of some sort.
I don't believe in "too much gun." My .375 was great on my Grysbok. If you are worried about meat loss be careful of the type of shot you take.
To me, the difference between the magnums and the non is what your effective range is. So in your example it just means that the wsm can do the same job further out than the .270. I'm simplifying, but it isn't too far off.
If you're looking for one rifle to "do it all" I've chosen the .30/06. It can handle any non-dangerous game out there. That being said, this is all part of the fun! Arguing what is best and trying different rifles. I LOVE my 06, but I'm trying to decide between .300 or .270 win for my next rifle, or should I just go with the plain win mag???
P.S. I also want a 1000 yard gun. That is a complately different rifle in my opinion!