We test rode both, and ended up with the Xtracycle RFA, but that was mostly because of comfortable fit -- we're both picky and fitting two picky people on one bike is even more of a challenge, although at least we're close in height/reach. (Definitely recommend the Performance CX motor, on whichever bike; as it happens, the GSD we test rode had a nicer motor than the Spicy Curry, but we were going to order the CX independently of which bike we bought.)
The GSD rear bags are excellent, by the way; we liked them better than the ones Xtracycle sells for the RFA so we finagled them to fit. In general, you might want to look at the accessory options -- they're both good bikes.