Im not sure Roy could beat him
Roy's good but at some point its a blown up MW against more than he can hande
Duffee's speed, movement and power is better.
Speed and movement, yes; power, no. Roy has some of the best one-punch power of any HW, and that includes the likes of JDS, Carwin, Overeem, Hunt, etc.
However, I do think Roy will eventually lose to a fighter like Schaub/Herman/Mitrione/Duffee. All of those guys are faster, more mobile and have a longer reach. It's just that they keep getting lulled into brawls, and Roy is so dangerous early in the fight. (Notice how almost all his wins come in the 1st round).
One of these days, a mid or even lower-tier HW will fight smart and "elusive" and get a UD on Roy. They just need to stick-and-move, circle away from Roy's right and land enough jabs and leg kicks. They may hear boos from the crowd and get called names on Sherdog ("too elusive!" "that boring Condit-Diaz gameplan!", but it will work.
With that said, I wouldn't pick Duffee...yet. I need to see more evidence that he's improving and has a decent fight IQ.