To be honest I cannot see Itachi standing a chance of winning. Base Itachi, looking at the panels, did not stand a chance, Sasuke kept up with him perfectly. Anything that required the Curse Seal can easily be replaced with Susanoo.
Now, I know Itachi is likely to use Susanoo more often when he's going all out. However he is still constrained by his infamously low chakra pool. That gives Sasuke a very clear advantage; he can freely switch between Taijutsu and Ninjutsu without having to choose wisely or spending a short amount of time on one art.
Sasuke has more scenarios in his favour e.g. if Itachi ignites Sasuke's Susanoo, then Sasuke can overwhelm that Amaterasu with his own (he can pour more chakra into his Amaterasu; more chakra in a jutsu is why Sasuke beat Itachi in the Katon clash)- but it won't end there. Sasuke can then follow up with interest with Kagutsuchi; it will give Sasuke a very easy opening to try anything else like his Susanoo arrows.
In the end it will be a clash between their highest level of Susanoo. Sasuke wins that, hands down. I say that confidently because rather than engage in a sword fight, Sasuke can literally keep spamming Enton Magatama till a few get lucky and Itachi will have no choice but to shield himself. It doesn't help Itachi that Sasuke can still manipulate the flames with Kagutsuchi.
Nothing stops Sasuke from setting up and using Kirin while making use of this "spam" seeing as it has been shown that Susanoo can be considered a separate entity, of sorts, from the user. Or he can let the Amaterasu flames do their magic and let them set up the conditions, wherein it'll only be a case of putting his hand up.
Nevertheless, in a clash between their highest level of Susanoo, I think the Enton Magatama spam alongside Kagutsuchi is more than enough to overwhelm Itachi.
Ironically, Itachi would be better off not encouraging Sasuke to use his highest Susanoo.
