I know it is an old thread, but I want to prove I did a search first.
Now I have always read that line length for stout faucets don't matter. My beers I serve on the beer gas don't settle until I take a sip or two then the 4 finger head slowly dies down then I can top it off and repeat. I use the same line I use for my regular co2 delivery which is 15'.
It there anyone out there with some tips? Do I just need to do a protein rest with beers I want on beer gas? Right now I have an IPA on it, tastes great, but I think maybe I have too much head retention? Once I take a drink or two it settles down though.