Yup.
If you compare .270 and .280 (and you might have reason to do so if you want to know whaat you can REALLY do with a .280), you compare sectional density of different bullets between the two cartridges. The bore diameter is close enough to be a non-factor in that instance, and you can pretty confidently use .270 data to estimate the safety margins of the .280 cartridge by using sectional density to establish some kind of equivalency. On the other hand, you could not use sectional density similarities between .30-06 and .270 to extrapolate a 65000 psi load for the .30-06 because of the difference between bore diameter between the two.
