Got a buddy that swears 20" is all that's needed however I'm inclined to use a longer barrel for more speed. I've settled on a 1/10 twist
The key to this question is intended application. The .308 can be run a myriad of different ways, for different purposes, with different results.
Like you, I prefer longer barrels. I shoot 1000 yard F-Class using 155 Sierra Palma bullets @ 2990ish from my 26" barrel, which is about as hard as I can push them. They are just starting to go transonic when they reach the 1000 yard mark. Palma shooters often use 30" barrels to allow them to push the 155's to 3000+ more easily.
For shorter ranges, out to 600 yards or so, the shorter barrels shoot accurately and the velocity loss is less important. In a hunting application, the .308 isn't going to take you much further than that, so you can get away with a shorter barrel.
Regardless of barrel length, you are on the right track with a 10 twist, which will let you take advantage of the full range of available bullets.
IMO, maximum versatility and utility in the .308 is obtained in 24" to 26" barrels. If the rifle is going to see more specialized use, longer or shorter than that may be called for.
I've had a 20" and a 24" .308 Win. Both shot 1 ragged hole groups. For a strictly hunting rifle under 500 yards, 20" is more than enough tube. For a rifle that will mostly be used for long range and as a target shooter/range toy...24-26" is best.
These are just my opinions based on my own personal experiences.
Hey MudRunner, what are your thoughts on a 1/9 twist 24" MTU for 185-200gr for steel out to 1200yds? Cheap plinker for target? Creedmoor , SAUM and STW are alot more expensive to feed. We wont even get into STW cost. You know that well.