There's a GREAT thread over on TGR right now comparing the Duke, FR+, and NX21. You can find it here: http://tetongravity.com/forums/showthread.php?t=111768
For what it's worth, I wouldn't recommend the Duke unless you're doing a lot of resort and sidecountry on these skis. I've seen a lot of people around here dying on the climbs because of that tiny thing Marker calls a climbing bar on them. It just doesn't get your heel high enough to weight your skis right on the steep stuff. I'd call the Dukes an alpine binding with a touring option; they're definitely a comprimise. Good binding, but not for everyone.
I'd also pick the NX21's over the FR+ (already did, actually). They tour better, are more torsionally stiff, and are a bit lower. I did a review of them here: https://newschoolers.com/web/content/reviews/action/read/id/548/