Can't comment on the R bit but I had a K1200S and now have a K1300S. They're both great but very different. The 13 is better in every way - power, torque, brakes, suspension and is, consequently a lot quicker on the road. BUT it doesn't feel as quick. The 12 made its maximum power at 10,250 and the 13 makes it at 8750 (IIRC) and the power delivery of the 12 was ludicrous. It started to make power at 4k but at 7k it all went mental - hitting 7k in 4th gear on full throttle is an experience! The trouble was, I ended up riding like an LC350.
If you want a fun thing to blast about on sunny Sundays, buy the best 12 you can find, if you want to use something as your main transport (as I do) get a 13.
Buy one of them though, they're not to be missed!