721's are good rifles the precursor of the 700 action. The M670 is just Winchesters version of the Remington 700 ADL, just the 670 has a better safety IMO. There isn't anything you can kill with a .30-06 that the .270 can't. I'd keep the .270 and give it a chance on your next hunt. What are the chances your .30-06 and his shoot your hunting ammunition the same. So if you are going to take two rifles on your hunt why not have two different calibers?
A .270 running 150 grain premium bullets is just as good as a .30-06 running 180 grain premiums. You give up a little frontal diameter but have nearly the same BC and SD and gain a little in velocity to help out the energy.
Nosler Partition
.308 180 gr, BC .474, SD .271
.277 150 gr, BC .465, SD .279
Federal Premium NP ammunition
.30-06 MV 2700 fps, ME 2913 ft/lbs, @ 500 yds 1837 fps, 1348 ft/lbs
.270 MV 2830 fps, ME 2667 ft/lbs, @ 500 yds 1928 fps, 1238 ft/lbs
Seems to me to pretty much be a wash as far as performance goes.