Since I used to dairy farm in my younger days, here's some advise I was given about how much silo storage to buy...
Figure how much storage you think you'll need today (+/- 300 yard shooting) and then add 50% (when longer shots are needed) incase a bumper crop needs storing or more cows are added on.
Bottom line...within 500 yards, both the 308/6.5CM will work, the edge given to the 6.5CM due to its more speed, as speed kills over bulk, as I've read.
Shots over 500 yards...the 6.5CM will shine, with its speed/accuracy advantage.
I'd built a rifle with the maximum range in mind, as it will handle any shorter ranges as well.
IMO, a 6.5CM covers all the shooting ranges you mentioned and then some.