Lardy, ballistics and rifles are not my strong point, but in my opinion I would say generally the .243 would be a little light. Depends on the area you hunt in SD, but I have been faced with some longer shots in SD and a .243 would not have the oomph I’m looking for to consistently bring down a whitetail or Muley. Sure if you hit a deer where you are supposed to you should find him, but we all know not everything goes as planned.
Again not being a ballistic wiz, I would probably guess something like a .270 would be a great gun for you. A flat shooter for those longer SD prairie shots, enough power to take down a deer, and I’m guessing not enough to do too much hide damage???? Good Luck , you might want to try posting this under the “Shooters Test Bench” forum and let the Ballistic Gurus try to answer this. Good luck!