The K2 feels much more lively, much of that is due to brand new tires and less weight. The lower bars were quite noticeable. We just installed the DSS electronic ignition and the engine runs much better at all rpm, especially at idle. Throttle response is much better. The seat is a little more slippery but the old foam doesn't support your weight as well as teh new seat on the K6.
The K6 feels a little porkier. Some of that due to older tires and some due to the weight from the accecories. It shifts much smoother than the K2 (and has 25,000 more miles). My throttle cables are obviously more worn as more effort is required. The windshield makes riding more comfortable but the view isn't as nice.
It was interesting to ride an un-faired bike again (haven't done that since I put the fairing on mine last fall). It made me yearn for the nimbleness of my 350. Hopefully I get a job soon so I can get it put back together and ride it. I'm thinking of adding 400F bars and foot controls to make it a little racier so then I will have my "sport" bike and my "touring" bike.