Sorry about that. Assume in situation 1 Deidara has it and in situation 2 Deidara doesn't. How do you think it would impact this fight ?
Okay, I'll give just a basic idea of how i think both fights would go. Or more accurately, How Deidara would fight in both Scenario's, since Onoki wouldn't really change battle styles in either scenario due to it being basic knowledge.
Oh, and of course, who i think wins. I'll go further into an explanation if anyone decides that they would to refute.
----
Scenario 1: Deidara has C3
In this Scenario Deidara would more than likely try to use this as the finishing blow, Since unlike when he fought with Gaara, He doesn't have to capture Onoki. The Reason for this is since he had it prepped before battle, he basically has a Bijudama level attack that he can use for free.
Now, Two things have to be accomplished for C3 to catch Onoki.
1. Deidara has to have Onoki in the Blast Radius while he himself is outside of the radius.
2. He obviously has to be above Onoki, and quite a good distance.
This can be accomplished in a few ways. Although it will not be easy since the fight has a high probability of taking to the skies and Deidara has to tread lightly to accomplish the above requirments. The Easiest way would be with a Nendo Bunshin.
You must be registered for see links
This same tactic that fooled an experienced sharingan user would surely fool Onoki. (also note he was able to fool 2TK Naruto with a Nendo Bunshin)
By the time Onoki Relizes that its was a kage bunshin Deidara has already dropped C3.
Deidara Wins this Mid-High Diff.
----------------
Scenario 2: No C3
In this Scenario Deidara would fight Much More Aggressively. Deidara would more than likely go for a C4 kill than anything else. Since Onoki is primarily a Ranged fighter. The Same Tactic that worked on Sasuke (and would work for C3) wont work here. Onoki wont come within range of the small C4 Nendo Bunshin Bubble. Therefore, Deidara would have to rely on the Garuda to get the job done, and it will do just nicely in this situation.
Due to the massive size of the Garuda. Onoki's Jinton wont be able to cover the entire Jutsu. Some C4 Is bound to escape. Intel Also dicates basic knowlege, Onoki will just think he stopped a massive exploding Nendo bunshin. Completely Unaware of the roaming C4 in the Air.
Deidara takes this High Diff.
-----
These were really short explanations and what I thought from the get go. I could possibly change my opinion once i see more of the debate.