As said, barrel length is not relevant to accuracy.
It is to velocity, with some calibers being more sensitive to "fps loss (or gain) per inch" than others; the .308 is relatively insensitive and most say about 20 fps per inch, or so...
There are a lot of long range shooters running 20" (and shorter) barrels on .308's, but if it's a bench gun (like mine is), the extra length isn't an impediment, it's an advantage- as is the extra weight of the barrel.
Natch, if you're shooting long range, why not get all you can...my new barrel is 26" on my 7-08, and I'll get a chance to chrono the same loads I was getting 2600 out of my 20" barrel next week. Still trying to get used to the feel of the rifle with a 5-1/2 pound barrel on it...
Only possible downside on that barrel is the 12 twist, I prefer a 10 on the .308. But, unless you intended on playing with pills heavier than 190 or so it shouldn't be an issue.