Don't know your feelings about naked bikes, but the R1200R has so many accessories available in the aftermarket, you could make your own lightweight tourer. I had an R12R before I got the K. I set it up early for performance, and fun in the summer. Before the weather turned cold, I bought heated winter jacket liner, a taller windscreen for more protection. I had roomy Givi hard side cases and a large tail bag. That bike is very agile and controllable in twisties and with 109+hp and good torque down low, it will romp. With the BMW sport screen (an amazing amount of protection for such a little thing), you can ride through strong downpours, with raingear, with no problems... I took it on a long trip with just that. The bike weighed fully fueled at 490lb with the full Remus... that's 70lb less than an RT and a lot less bulky.
Here are 2 variations of the bike (custom-painted) in its different travel modes:
This is the way I rode it in warm weather and when in "sport mode." Had the light full Remus exhaust & a Dobeck fueling module, and Michelin Pilot Road 2's (superb).
This is for the longer travels and/or winter. 18" Cee Bailey screen. I could remove/install the Givi rear mounts in less than 15min so I rode the bike with them off 90% of time to keep it really light & naked. Givis are half the price of BMW hard bags.
BMW site states the F800ST is 461lb fully fueled, and my R12R was 490lb in lighter trim fully fueled... not much difference in weight between the two and R12R has a whole lot more "snot" to it. Anyway, just something you might just want to put on your consideration list. Otherwise, you need to think Japanese if no Beemer in your plans.