the sniper country article that was posted is so old and outdated, that with todays rifles and calibers it doesnt matter... I was also looking into a 1000+ yard shooting caliber, then I went to a 1000 yard match and saw how far that it really is... Oh man!
Out of the .308 and the .30-06 I would chose the .30-06...... reason is the bullet availability, and with reloading the .30-06 can stomp the .308 in competition. I have seen both calibers perform well at long range, withthe edge going really neither way... its not the caliber, but the shooter. If the shooter doesnt undertand wind, ballistics, range compensation, and even elevation, humidity and other aspects taken into account for a shot that long, it wont matter what gun he has in his hand...
I like the idea that on average, no matter the yardage the .30-06 has more dropping power and penetration at longer ranges.
so either way you go, both calibers will do fine. Just make sure your doing yor part because if you dont do your part, dont blame it on the caliber or gun.