+8 simon or over 30 seems like a reasonable play here.
as a comparison, nishikori is also +8, but against nadal. yet, simon is better than nishikori and federer is worse than nadal, so the underdogs having the same game spread is puzzling here. simon is the kind of guy who will gladly give up if he is behind in a set, meaning federer has almost as good of a chance at a double break as he does at a break per set. however, simon is also a guy who plays to the level of his competition. he looks sleepy against inferior opponents and rarely beats them by the margins that he should. but, he also appears invigorated against superior opponents and raises his game. +8 covers a wide variety of federer 3 or 4 set wins.