To give a proper answer I'll have to rewatch highlights, but for now I'm going to have to say ROX would win.
I remember ROX was the top seed going into World's. SKT beat SSG in the gauntlet before losing to KT Rolster in the semis, who then lost to ROX. ROX had a scary good roster all around, while SSG had a couple players who weren't quite as good individually.
ROX also had SKT down 2-1 before Bengi was subbed in and saved the day. (Blank was never better than him and they should have replaced him)
Meanwhile the SKT/SSG finals was just crazy dragged out. SKT got a lead and it took a lot of turtling and time for SSG to exploit death timers to win two games to force a 5th game.
Like I said, I'd have to go rewatch highlights, but I think ROX was just better that year and would have eliminated SSG if they played.