For me, if you already have an 850 then the 900XR isnít going to be much different as itís basically a slightly bored-out version of the same engine with 10hp and a few Nm torque extra, which will steer quicker due to the 17Ē front wheel. To me as a road only bike this would have been much better without a chain as it would have made a great tourer. I was a previous owner of both the F800ST and GT and losing the belt drive (despite its shortcomings) is IMHO a backward step. Shaft drive would probably make an already heavy bike for the engine size even more porky.
Given that itís only £3K or so cheaper than an S1000XR, and that bike is a not dissimilar weight and far more exciting than the 850 series engine, other than those whose budget simply cannot stretch to the S1000, I canít see who would want the 900?