Navas would be great in the Johnson impact sub role, but Pellegrini likes him as a starter. He's had some cracking games, but can be very ineffective too.
When I look at our team, I wonder if Reus could add that extra pace, trickery and directness down the left, with Nasri moving elsewhere on the pitch if we play only one up top.
Dortmund play a very direct game though, so who knows if Reus would slot into our system as seamlessly as at BVB. His pass completion is worse than everyone in our squad bar Dzeko and ball retention seems to be what our club loves (the Barcelona way).
Just seems, though, that most top clubs have at least one fast, direct, 'scary' player... Di Maria, Bale, Neymar, Pedro, Robben, Ribery, Hazard, Walcott, Sturridge, Reus. Navas is our closest thing but doesn't really go at players like these and scare teams.