However, if you live in more open plains...I'd pick the .270 for the flatter trajectories and reduction in recoil over the 30-06.
I do like the 270. However, its recoil is not much less than a 30-06.
Load a 30-06 down to the 270 bullets and you will have a similar trajectory (so close as not to matter as once past 300 yards the drop gets to be so much its a mute).
On the ohter hand you can load 270 up to 180 grains and have a good short range match for the 06.
And not a 30-06 is not my first choice for a grissly, but far more have been taken with that than all those magnums.
And comparing black powder balls into a bear vs a modern bullet is invalid.
I know of one case (Elmer Keith) where the bear came after his party. Upshot was that they saw it and 5 experience hungers hit it with anything from 35 whalen up to 338 mangum. It finally died at their feet (fortunately an uphill charge by the bear). You never know about a Grizzly. I would guess only 5 rounds from a 50 caliber would drop one for sure.