This is my humble opinion.
RoadKings are great bikes, if that is what you're looking for. I rode my friends a couple of years ago and took it for a 20-30 mile run. At the time I rode a 950 so it was all I had to immediately compare it to.
It has a lot of power, that can't be denied. It's heavy and it felt heavy to me. The clutch would be impossible for me to deal with, PERIOD. It wasn't a balanced ride for me. The seat was back too far and the handle bars were to far front and low. I had a lot of issues trying to get the kickstand deployed. Once it was going, the ride was very smooth in fun. Brakes were inadequate for the weight of the bike.
I don't count gears when riding I just keep shifting until it won't anymore and I still tried shifting in the top gear of his bike. A sixth gear in not nirvana for me.
I wouldn't have traded bikes with him at that time.
I now have a Liner and love it more than my 950. It's heavy, but doesn't feel heavy. It's center of gravity is pretty low which makes this bike a pleasure to ride. All of the turns that made me sweat on the 950 can now be navigated 5-10 more mph faster without my heart coming through my mouth. Power, wow power! It rivals that of the RoadKing if not betters it. It puts a smile on my face everyday. I ride a 9 mile stretch of interstate on my way to work everyday and sometimes never hit 5th gear, however in other instances I shift to 5th and then try to shift to 6th. This is me not knowing which gear I'm in, not the fact that i feel I need more gears.
It's easy to road test a Harley, but not so much a Yamaha. I don't how to answer your question any better than I've already attempted. I would not trade in my bike for a RoadKing or any other HD product. If I had the money, I'd maybe have a Street Glide or Electro Glide in my garage for week end excursions, but not for longer trips. I came up through the ranks riding with HD owners and I always had Yamaha's. We spent hours on rides tweaking their bikes. I know this may sound like Harley bashing, but it's not. I rode their bikes and loved them and always thought that maybe I'd have one someday, but even then I knew it wouldn't be my only ride.
If you want 6th gear, buy the HD, Victory or Indian, but I don't believe that alone is worth the extra $$$. If the other features add value to your ride (not gagetry), then they may be the bike for you. It truly is a personal decision. That's why there are this many choices out there.