you know, i forgot to include marcum on my list. i think he's a push. i think in a real-life draft, 6th round is a bit steep for him, because i don't like paying up for pitching. he's 77th overall in the yahoo game, so that's just about 6th round. his FIP is also 3.64, above his ERA, which suggests some regression next year, because why do the brewers play good D for him but not grienke (FIP a run lower than his ERA)?
keeping marcum probably comes down to how much pitching gets kept in your league. if there are a lot of good pitchers available, then definitely don't keep him.
in absolute terms, gun to my head, i say don't keep him. but i wouldn't think you were making a big mistake if you did.