I would pay him $15 mil for 4 years with a club option for a 5th. I might go as high as $16 mil per, but not higher. He's young too, so it's not like he is in his 30s with a ton of milage. It also allows us to trade Porcello or leave Smyly in the minors incase of an injury. It also gives us another year to evaluate Fister and Max to see if they are worth keeping long term.
edit: Remember, pitching and defense wins championships. We just witnessed that first hand.