Right now, I have a 10" Ilex Paragon (Portronic) in barrel, and use a top hat shutter. I have plenty of bellows draw to go much bigger, Calumet cc-401 w/22" bellows, and a Cambo w/18" belows. The cc-401 will get you in closer than you will ever want to be, the extra long bellows is great for macro with the right lens.
My favourite 4X5 head-portrait lens is my 360mm tele-xenar, which doesn't require full extension. My Linhof SupTecV has more than adequate bellows, so that is not a problem.
I suppose I could get a clear shot of nose pores and pimples if that was the challenge, but I haven't tried yet.