The .30-06 is more than adequate for Plains game in Africa and it takes 700-800 pound antelope every day. I agree with you that the .30-06 is overkill for whitetail deer. However the other cartridges you mentioned are of nearly equal overkill.

I personally recommend the .260 Rem for deer...or the equivalent things like 6.5 X 55, .257 Roberts, .25-06 etc.

At least with the 7 MM or the .30-06 you will not have to buy another gun for elk or other non dangerous game.