Well, The R1250RS turned up early, and I have finally managed to get out for a first little trundle.
First (non - test ride) comparisions with the K1300:
It may be smaller but its still made of BMW lead and a hefty lump to wheel about; the TFT dash is excellent (best Ive seen) and functuonality comprehensive and requires a bit of homework with the handbook. The motor is a peach - Road mode is ideal for town traffic hell and the full fat dynamic mode gives very little away to the K's turbine like delivery, at least at legal-ish speeds. The motor also has a bit more 'character', in that it doesnt feel like a big electric motor (but then I'm a twin fan, my first boxer though). Oh yes, and its a lot harder to get on the centre stand despite being smaller and (a little) lighter - somebody got their geometry a little off.
All in all, so far I'm dead chuffed. When I've done a bigger ride on it I may have more to say (some hope this year now as they've started gritting the roads around here.......)