I've got them from 18 to 26, and everything between. 20in can safely run mid 2900s with heavies in most weather conditions using standard powders. 18in I run mid 2800s as wet weather gives psi signs above that. Nothing wrong with a 20in using a short oal, or OTB supressor, I think it has the most balance of speed without really stepping on it.Just came to say I went with a 20” 6 creed and regret it, should have gone 18” or shorter
I use rl26 in one my 20in barrels and never found pressure till 3100mv with 109s.
All depends on what your goal is mv wise, if you're good with 2850 2900max, 18 is all you need.