In 2011 at least, in addition to the leather vs. hard bags, the RKC had the 103" motor when the RK had the 96", the RKC also came standard with ABS and the security system, which the RK did not. In 2012, I'm not sure there were many differences.

 

For my old Road King Classic I had 3 sets of bags, 1 perfect stock leather , 1 beat set of leather with locks, 1 set of Police Hardbags. It is easy to switch and fun to change the look of the bike. I think you can cram more odd shaped stuff in the stock plastic/leather ones but they sure are no good in the rain. None of the bags are really secure as long as you still have the quick detachable clips though. Pop 'em with a screwdriver and take the whole bag right off the bike. You want the secure you have to put at least one nut and bolt on each bag. I used a bolt from the outside and a good nylock on the inside just snug enough to barely compress the rubber washer and if you tried to put a wrench on it from the outside it would just spin. Maybe overkill but I sure slept better when staying at a hotel and my bike was not near. I also would take the bags off and in the room with me along wit all the other QD stuff.

 

It's not just the bags. You might want to do some research on the differences before you pop off so intelligently. Google is the best!!