What if Question was investigating case of Kira
Hmm... tough call. The Question hides his face and is probably paranoid enough to do that that would make finding out his real name a time consuming task. If it's just a physical fight, Question wins. If it's a battle of the wits where the goal is for the Question to link the Kira case to Light with solid evidence or Light finds out the Question's name and kills him without bringing suspicion to himself, I think the Question will last about as long as L, but still die in the end.