Asking these guys about the R12R is like asking a Russian where the best vodka is made.
If you lurk over here like I do.. you'll notice the: squishy, huggy, warm and fuzzy topics like: "I love my bike" or "Is this the greatest bike ever?" or "how do you show your mototcycle that you want to sleep with it without coming on too strong?". There was a time, before the R12R section was made (or the bike) that the R1150R section was full of that stuff too.
I have avoided a test ride on the R12R just to keep my mind off the thing. I might think about a used one down the road...but I'll probably go for a bike with liquid cooling (almost certainly Japanese

)when the time comes to add a bike or replace my R1150R.
I think it's fair to say that if the R1150R fits your needs and desires for a bike, the R12R will do the same...only better.
Some things the R12R will do a little better, everything else it will do much better. The biggest difference is the motor...the 12's motor is far superior. The second biggest difference is the lighter weight making it better handling. Putting the two together means significantly better acceleration. The 12 seems like a much more durable bike too, but the fleet is obviously newer and has fewer miles.
I was dreaming when I wrote this, forgive me if it goes astray...