The thought that Edmonton could go Crosby, Malkin, Drai, Nuge down the middle would make them terrifying offensively, but feels to me like there'd still be some pretty big holes on the team. Ignoring the cap, if they thought this would win the cup this year or next, they'd be silly to not take it.
But Crosby and Malkin are at or near that line where age will start slowing them down. I mean, 38 year-old Crosby is probably still a damn good player, but he won't be in the running for the Rocket. Long term, the deal probably swings to Pittsburgh's favour.