I have a 4 I use on a 8139 Burkie and it fits it well. Very nice reel, great drag, can also be palmed, solidly built and works fine in below freezing temps. Have one complaint and that is when stripping line it does make somewhat of a high pitched noise.
Location: Idaho - Clearwater River, St. Joe River... all the others too! California -Lower American River, Truckee River, Little Truckee River, Mokolume River
I have both reels, but am only currently using the 3.5+. As a general rule Iím finding that the 3.5+ is fine for 7 or 8 wt. rods. However, specific conditions matter and (I think) balance on a specific rod is a good starting point. If this was my situation Iíd weigh the Battenkill V and compare itís weight the the ARX reels and go from there.