Of the cartridges you mentioned the only one I don't own currently is a 7x57 and I wish I did in a classic configuration. I am a big fan of the 7RM but don't shoot it much now as I don't hunt anything larger than deer and hogs as much as I used to. The 270 WSM in a feather weight configuration is another favorite, even in a feather weight carbon McMillan I really don't notice the recoil difference from the 270 Win. until after about 40 shots or more.
I would say trade them all and get one nice 6.5, 6.8, or 7mm in a really nice rifle. You are talking about .02 difference in caliber and +/- 200 - 250 fps velocity. A little more spread for the 6.6x55 and 7x57 vs the magnums, but not so much that there is a huge difference in the field.
If a shoulder issue is the deciding factor, and it could be soon for me, the 6.5x55 would be a top choice as is the 7x57. The 270 vs 270 WSM is mostly a paper ballistic debate, the 270 WSM could be more accurate, but not that you could tell in most hunting rifles. If I were to spend a lot on a custom rifle I would probably go 270 Win. in a classic wood stocked rendition.
