Some consider the Road King the "coolest" of the touring models. The Heritage you have ridden is a softail; hard mounted motor with crank shaft counter balance mechanism to smooth out the crank vibration that is inherent with an odd firing, 45*, vtwin motor; often referred to as the "B" motor.
On the other hand, the touring model motors are rubber mounted, no crank shaft counter balancers and are often referred to as the "A" motor.
The difference you will notice between the two is that at idle, the "A" motor is going to move around in the frame; however, once off idle and up to cruise rpms, the "A" motor is smooth as butter. On the other hand, the "B" motor will not move around in the frame at idle but at cruise, say 70mph, there is a noticeable "buzz" in the handle bars and foot pegs. Some softails will buzz more than others but you won't notice the buzz until the end of a 500 mile day.
Can't say anything bad about a Road King. You should have a dealer run the VIN through the computer; any work done at a dealer will show up. Cam chain tensioners could be a concern but those can be changed and upgraded cost effectively and worth doing.