His trifle with Deidara has perhaps been the only one on one fight where both have been at their full potentials if not quite there.
The matter of beating Itachi has been settled by the plot of the manga itself, whether it is to be argued as the ramblings of a character or not, in seeing its factual basis by that it was placed as a minor value by Kishimoto as is many minor sentences and explanations to clear the mystery of a smaller plot so that the fans are no longer frustrating themselves with the same irritating questions that have remained unanswered:
You must be registered for see links
In the fight against Danzo, I would wager if a fair fight had been the true matter, Sasuke would have in high probability lost to Danzo in managing to lay a severe injury upon him. Although, it is be in popular agreement that if Obito/Tobi had not been a factor, nor Karin, Danzo would have instantly been the greater sword in such a fight and possibly not even required the use of his KA trump card.
His slaying of Orochimaru at the time is far less than an achievement that can be boasted, as many others would have likely to have been able to defeat him[, some without being caught within the transference ritual's reality inside the Serpent Sanin]. Nevertheless in seeing how sick Orochimaru had been, the battle was a mere cunning feat of using a situation of temporary disability to one's utmost advantage, relying more on plot events if anything.
I would stray further upon other characters he has lost to in fair fights, including Rock Lee and Gaara in the original series, and especially Killer Bee despite all the advantages he had gained in reinforcement of his team. However I believe I have rambled on quite enough and leave with a single memorandum:
"I find it an embarrassment that he and Taka had become part of the Akatsuki. Damn you Tobi..."
nothing more