I would never recommend the 243 as a deer rifle so I couldn't give a thumbs up to its slightly bigger cousin. I put the 243 in the same company as the 223 and 22-250.
Well, the .243 might not be enough rifle for deer for a damnyankee, but it's sure plenty good enuff fer us rednecks! Seriously though! The Eskimos shoot polar bear, walruses and seals with .22 Hornets and .223's all the time! They're all handloaders with no money, and can't afford to burn a lot of powder.
Most of the problem was with the first bullets that came out in that caliber.
Elmer Keith believed the .30/'06 was inadequate for jackrabbits, too, and the reason was poor bullets in the early loadings! They loaded .30/40 Krag bullets in the '06 case, and drove them 500 FPS faster than they'd stand up to.
IF you use a proper bullet, and hit the proper spot, it doesn't make much difference at all as to the diameter of the projectile. A 106mm recoilless rifle won't kill anything either, if you miss the target with it.