The difference between a 7mm-08 shooting 140's and a .270 WSM shooting 130's is about 1" difference in drop at 400 yards. Shoot the 120 grain TSX out of the '08 and I believe the trajectory would be the same.
I am sure you are aware of this, but I came very close to going the same route with a WSM and ended up with a simply boring 7mm-08 that has very little recoil and shoots lights out.
With your requirement of a factory gun and a WSM I would shop around for a used Remington titanium mountain riflre in .270 win, have the action trued and barrel set back and re-chambered as a WSM. With the long action you could get the maximum out of the WSM and still be at 6 lbs.
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