RE: .308 or .243
Every rifle shoots certain loads differently. As to wheather the .308 or the .243 is the better round, either will work adquately at 200 yards. The .308 holds more velocity and retained energy at 200 yards + , but either will work. The rate of twist will be basically the same in rifles of the same cal. They all have this down to a science, so the best rate for the cal. is not a guess anymore.
If you are looking for personal preference.... I would go with the .308. It will do everything you want it to do for deer, and also other game as well if you decide to shoot longer distances or hunt for other game in the future.
MET