Orochimaru, who is a mid-high kage level ninja, takes part 2 Sasuke's body. Let's see...
When Sasuke took Orochimaru's powers Oro was in a weakened state so he wasnt as strong as he was. Orochimaru would've become healthy after he took Sasuke's body.
Sasuke who was able to use the curse mark, has the body to be able to get dragon sage mode. Oro in his body would have dragon sage mode.
Itachi was sick at that time, so not only is Orochimaru far out of a healthy Itachi's league, Itachi is sick.
Plus the fact Itachi would want to save Sasuke somehow, and would hold back.
Itachi=sick, intent to revive Sasuke
Orochimaru= Sharingan to counter Itachi's genjutsu, lightning style, kirin, dsm, and Manda.
The result= Orocohimaru taking Itachi's eyes and getting ems. Itachi would lose horribly guys.