I think 20" is about ideal for 308 as an all around length. I have 2 with 22" barrels, but can't see enough difference to justify cutting only 2" off of them so they will stay at 22". I have one of the Ruger Predators with an 18" barrel. It is a little shorter than I'd prefer, but since I already have others with 22" barrels it fills a niche. If it were 20" it wouldn't be enough different than my 22" guns.
On 30-06 class cartridges 22" is perfect. I want no more, or less. I can deal with 24" on magnums, but I no longer own any and if I needed 26+ to get the performance I'd just have to pass.
If I had 24" to start with and wanted something shorter I'd probably compromise at 21" just to be unique.
