You will give up displacement as well; 103" to 96". Plenty of take off 255 cam sets available on Ebay; very close in profile to the "hotter" '14 HO cam. Don't understand "give up the bags"; both '09 and '14 Kings have hard bags. JMHO but you won't get your money's worth out of the Traxxion suspension. Call Race Tech and get a set of springs and emulators and rebuild your forks; get rid of the diving when braking. A set of Ohlin rear shocks will solve the "vague" feeling Sled Dog makes reference to; call them up and they will put a set of shocks together for your bike and rider weight and it will come with all the bells and whistles. I would also suggest you ditch the OEM Dunlops when the time comes and replace them with something more suitable like Avons or Michelins.
The gearing on the '09s was improved from '08 which was really too tall for two up touring. A very common modification on the '09 and up touring models is dropping a tooth on the trans pulley; 32 to 31.
I don't hang off the side of my '02 FLHT like Sled Dog but do push it. I have replaced the 16" wheel with 18" wheels so I don't drag stuff near as often as I used to and I have slowed down a bit as well; getting to old to ride like I did 25 years ago.