Hmmmmm! I've only done a few extended vacations on my FJR.
Moscow, Idaho (3 days there, 2 days riding, 2 days home).
Skagit, WA: 3 days riding there (Peak to Peak ride: Donner, Lassen, Shasta, Mt. Hood, Mt. Saint Helens, Mt. Ranier) and riding to the Canadian Border to Mt. Baker and Whidby Island. 2 days home.
A couple of longer vacation rides, of over 3500 miles, to Park City, UT (via Idaho, Sawtooth Mountains, Yellowstone, Grand Tetons. Home the same way except Hells Canyon to Bend Or, then home) and then to Golden, CO.
In this mix were a few 500-600 mile days.
But then, I've never taken a cruiser on long distances. And the Russell seat and travel footpegs do help immensely.
Aaaannnndddd....there are a number of owners here who've done these types of rides 2-up. From the local area: Bluestreeks, uberkuls, Highlanders, Ric-in-Sacs, Hycles & Rogdebs, most of whom were on our little Jan 3rd ride.
The best advice is to plan some 3-day weekend trips and see what you might need to modify for comfort. Then load the FJR and enjoy your trip!