Despite what most people think, short barrels are not ideal for long range work.
Yeah, you can get hits, however, in any sort of windy scenario, your hit percentage goes waaay down.
If you also anticipate running your rig in a precision match, the short barrel will be an impediment. The serious long range shooters do it with 30-32" barrels for a reason.
If you must use a 308 at distance, don't handicap yourself...get as long a tube as you can. You can always cut it back in the future, but you cant add length to it.
One more bit of advise; Ditch the 175/168s...I'm assuming you are talking about Sierra Match Kings. While accurate, they are an outdated bullet design and really hobble 30-cal performance.
I am a big advocate of the Berger 168 & 185s. They are MUCH better options for range work in 30-cals. They are pricey, but conistent, with sky-high BC ans makes getting to 1,000yards with 308s much easier.
A more economical choice is the 178gr Hornady HPBT (not AMAX). It has the same BC as the sierra 190gr SMK, but can be pushed about 100-120ft/s faster.
