A high caliber uchiha can stop KAItachi know about Ka ,that's good but using two shadow clones will also split Itachi's chakra in 3 ,it can works but riskly as well.
Itachi might use Crow Clone Technique,it requires less chakra.
But the question is will Danzo take the risk to use Ka if he isn't sure that Itachi is a clone or not?If Itachi uses Amaterasu or Susanoo, it would be with the real Itachi.
I think that both can win,but if Danzo fail with Ka ,Itachi win.
that makes no sense as sasuke did not beat him without alot of help and danzo holding backf Sasuke can beat him, so can Itachi...