I was wanting a AR10 for the longest time before I bought my AR 15's. .308 is a fine round and has it's uses for sure.
That said you can shoot a 15 more for the same cost and as far as distance for SD/HD 99% of use will never need to take a shot outside of 50 yards. The 5.56 at that range and more has plenty of power for small to medium game and 2 legged creatures do not stand a chance!
NRA Life Member, SAF Member