I think he'd be harder to get.
How come?
OM seem fairly happy to raise funds through selling at out of form substitute, whereas I'm guessing Saint-Étienne would be less willing to sell their in form star.
I think there's quotes from Saint-Étienne's president(?) from about a month ago, saying he wouldn't sell him in January. Not that that means it wouldn't be possible, but I imagine it would be more difficult.