hmm... but i thought the answer to this has been revealed? kakashi has attained a higher level in usin his sharingan while sasuke can only use it to detect high speed and predict movement... what kakashi did when he was battling zabuza was that he put zabuza under hypnosis... and gives him the impression that kakashi is copying his move simultaneously... but in actual fact... kakashi is copying at a speed slower than zabuza... but the sharingan fools the victim into thinking he was actually being copied at the same time... and kakashi can predict what his opponent wanted to say to fully fool zabuza... that's how kakashi's sharingan works while battling zabuza... but i believe that itachi's sharingan is much stronger and we probably havent seen the best of his sharingan yet...