i don't think sasuke will be able to kill itachi jus because he didn't acquire mangoukuu sharigan, i dont think any of orochimaru powers will be able to help sasuke, and not to forget orochimaru doesn't even want to help sasuke he jus wanted to take sasuke's body and prolly learn mangoukuu sharigan and all the other jutsu's

if u talk about who has the most potential to kill itatchi, i would say naruto ovious, jus because i doubt mangoukuu sharigan will work on naruto. don't forget kyuubi is also in naruto's body, my theory is if itatchi tries to use it against naruto, kyuubi will come and save him. like in the manga said "in order to break a gen jutsu u have to distrub the chakara flow of the body, and kyuubi in naruto's body which means it can distrubt the mangoukuu sharigan, and let talk about ability- speed, chakara, naruto definitly will have the edge...in the naruto and sasuke battle, naruto only released 1/9 of the nine tails chakara, considering kyuubi have nines tails and only 1 tail come out of naruto...

if naruto learns more jutsues he's already unstopable....and since he's the main character, it's ovious...