I think that the rifle choice should be one of the determining factors in caliber choice.
I own and use both the 270 Win. and the 270 WSM, my win is a pre 64 M70, a beautiful rifle
but heavy to carry compared to my WSM which is a Kimber Classic. I have carried the Kimber
more than the M70 because it is so light and handy, it is a beautiful rifle that makes good use of the WSM
in it's compact action and overall proportions, it is everything a WSM should be, this is the main difference between the two calibers
and of coarse there is a power advantage in favor of the WSM, we should not underestimate the ballistic advantage
of the WSM for long range work. I recently had the opportunity to shoot at 500 meters with the 270 WSM loaded with
140gr Accubond bullets and it's trajectory is very beneficial at times when we estimate a little short or if
the wind is not what we thought it was, that small ballistic advantage can make the difference in a hit or a miss.
Good Luck
BB