If Tobi was truly as strong as you state - at that given time, can you tell me why he didn't just absorb Naruto in the woods when he recklessly attacked him? He could have captured him so easy, and it wouldn't matter since Itachi would be gone later. Also Nagato knew all along, and so did Zetsu, it would be easy to still hide his identity to the remaining members of akatsuki... In general his skill and way to act has just been too random.
Itachi is determined, and he wouldn't miss a chance to kill Obito/Tobi if it appeared, however, he also thought it was Madara, and Itachi wasn't sure about his skills, which is the reason he never risked trying to kill him, since if he failed he knew he couldn't keep akatsuki out of konoha any longer..
Itachi is no doubt one of the smartest and thereby most skilled shinobi in history. His genjutsu level would exceed Obitos as well, how would Obito ever be able to kill Itachi? His only chance is to absorb him, but genjutsu will pown him, and at the right moment itachi will just strike.
Stop saying Obito is way over Itachi, I say we haven't enough info on Obitos skill in genjutsu and in fighting other sharingan users, since these sort of fights are very different. From what is known it's obvious that Itachi is more skilled..