If you plan to sleep in the back, definitely get the 6.5. If you're going to use a RTT, ground tent, or trailer, then just get the 5.5. I've moved from a FX4 F150 with a 6.5ft bed that I slept in to a Raptor with the 5.5 ft bed. I plan on doing a bed-rail mounted RTT. I'm much happier with the...