Interesting theory has been presented by several users on other forums. They're arguing that Madara's efforts to impede Hashirama from fighting Tobi have an ulterior motivation. He wants to acquire Sage mode. As we all know, the main weakness of the Jubi jinchuuriki is senjutsu. It's the one form of chakra insusceptible to Onmyouten. Could you imagine what the result would be if Hashirama were able to successfully use sage enhanced Mokuton against Tobi? This battle may have already ended.
So it's possible that Madara wishes to acquire either the knowledge to use or physical characteristics necessary for Sage mode so he can create an advantage for himself when he finally turns his attention to Tobi.
This was the panel depicting Madara as he was fighting Hashirama in #641. The translation is by Viz. I'm not sure how much validity there is behind those exact words though.