Here's something else to think about...
5 years, 42.5 million, 20 mil guaranteed.
That was the contract given to none other than Pierre Garcon. You know, the same Garcon that like Decker was dismissed as a product of Manning. Unlike Decker though, he never had as much success with Manning as Decker did (Garcon never reached 1000 yards while playing with Peyton). And last year Garcon had a great year, putting up 100+ receptions and 1300) yards with a one legged RG3 (and Kirk Cousins). He proved that he wasn't a product of Manning.
I don't see any reason why Decker can't do the same. And he's not even getting paid as much as Pierre.