Manda and other giant snakes could give Orochimaru the win, not to mention he could possibly deflect lower-level bombs through Fuuton. He could also bait Deidara with Kage Bunshins.
Also, seeing how he could tell Sai's ink clone was just that, and that Ink Clones are apparently difficult to see through, Orochimaru could possibly see through Clay Clones as well.
But anyway, C4 would definitely end it if there's no Intel. Orochimaru has the edge at first, but the longer the fight goes on the more Deidara gains the advantage.