I pretty much agree that the R bike is an RT light version.
I ride a 1985 R80 with a Parabellum wind screen good wind management,
had the opportunity to ride an R1200Rt and a R1200R back to back along with my own bike all in one day.
The RT was real nice but felt bulky and over weight compared to the other two.
If I were doing a cross country trip I would probably favor the RT due to the electric windscreen, but most times I prefer the more naked look of the plain R bikes.