Will be good to know which were the pro/con between the two and what was the main reason you switch (on both cases).
The V1K is really fast & strong, one can tour two up with luggage without any problems. It is amazingly easy to ride, you can never be in the "wrong gear" and it has really good brakes, twistys are no match for it neighter. Finally, its a great looking bike IMHO
The V1K have two power setups one "full" and one "Low" that delivers only 75% of the engines power. Well, I fail to see the use in this. Fuel economy is not much better in the "low" function. All it does is to make your bike go a bit slower. I used it in the breaking in period and never touched it again. Most of the guys on the V1K forum did the same. A function no one uses.
The riding position is not nearly as comfy as on the 650, granted that the V1K seat is thick & nice but its the ergonomics of the bike itself. I slammed on foot lowering pegs and bar risers but still not so nice as the 650.
Its a large and heavy bike, espesially on the garage way. I never learned to ride it the way I ride my 650.
But the main reason was the engine it self. For me at least, a bike should vibrate, it should almoust feel alive when your riding it. The V1K felt like driving a car on two wheels. Some people enjoy the in line four. I thought that I would, instead I ended up just useing the bike when I had to somewhere, rarely for any pleasure cruises.
Building-wise, both the bikes are of the same qualety as far as I can see, the V1K have more electrical gadgets and an aloy frame, but disk brakes rust just the same as on the 650. For me, less fancy stuff means less stuff that can brake and end up spoiling my vacation plans.
In conclusion, the V1K is a fantastic bike for those who enjoy this type of bikes, really good value for the money. One gets a bike thats equal to the R1200GS in every aspect but offroad, and seriously, how many owners really take the beemer offroad?