OK - well, my first thought (maybe it's my second or third) is that I'm not sure I would consider shooting at a deer at 300 yards with a 70 grain bullet regardless of whether or not it was legal. I guess I assumed that since your question has to do with ethics, not legality, that we would be talking about something with at least 1,000 ft lbs of energy. I know this is all a matter of opinion, but that's my take on it.
However, given the data you are using in this scenario, I would consider any of the roundballs at the ranges and velocities in your table to be more ethical than the .243 70 gr at 300 yards.

IM jaybe