Here we go again.....

Let's put a more practical twist on this than simply "recoil." Consider that the .300 and .30-06 are capable of throwing EXACTLY the same projectiles (bullets). The .300 simply pushes them faster (and farther as a consequence). If you intend to keep the .300, there's little reason to select the .30-06, and particularly in an ultralight.

My recommendation between the two calibers you list would without question be the .280. I'd be tempted to look into the .264s though as well.