6th in an 8 team league is ok, but later is probably more appropriate. I would take him in the 5th of a 12 team league for sure. Fourth is probably too early because of the injury concern, but in terms of ability, he may well produce like a 2nd round pick.
So in an 8 team league, his actual draft position might be higher, because you can afford to take risks after you already have four or five players, as opposed wo when you only have three.
Ability wise he's right up there with the top ten pitchers in the game, he's just so much of a wild card, that you should be careful when deciding to draft him. I took him in the fifth round of one of my 12 team leagues. I think that's the time to take him.