I have a 2013 RT - the last year before they came out with the OEM backrest in 2014. I am 6'3" with 32" inseam, and the standard seat made my knees bend too much. The OEM comfort seat set me back an additional 2" on the seat and made a huge difference in riding comfort for me. In 2014 they improved the comfort seat and actually made it more comfortable, so now it should be even better. I sat on one at a dealer and it seemed more comfortable than mine.
At SpyderQuest this year, I tried an Ultimate Tall Boy seat. It gives you 1.5" more room. It was comfortable to sit on, but was worse than the OEM comfort seat for my leg position.
If you don't want to spend the big bucks for a custom seat (which may give you both leg room and comfort), my advise would be to get an OEM comfort seat for your 2014. If you find that you need even more comfort for your butt, you can always get an AirHawk R air cushion. I like mine, but over this winter, I am going to insert one of Motorcycle Dave's gel pads into my seat. Hopefully that will allow me to get rid of the air cushion.
As for the backrest, as Steve posted above, they are not interchangeable. Since there is no backrest for the 2013 seats, I opted for the Utopia Backrest, and I love it. (I've included a picture.) You would have a choice of a new OEM backrest, or an aftermarket backrest like the Utopia, which costs less, and many folks find to be much better.