A really interesting subject to bat around -- I think the variables and percentages are too great with the 168gr MK and I don't think 26" will suffice... if you really want a 1000yd .308 cal hunting/target rifle... I'd mimic the concept of the Palma/F-class rifles. 1:14 twist, 28-30" length and 155gr VLD bullets. The Berger VLD would be my choice.
If you want the rifle more than the project... the Savage 12 Palma is readily available.
My own personal version of this dream is based on 6.5-284 -- however, since 1000 yd range is nearly inconceivable in my eastern mountains... I live out my LR hunting dreams with my .243win on coyotes across dairy farm pastures.