Tsimikas is very good going forward, his crossing is very good, probably better than Robbo, but Robbo looks the better defender to me, certainly positionally, but that could also be as his defensive colleagues are mire used to Robbo.
So against Chelsea, I think I would feel better with Robbo if he is fit now, still, nice problem to have to be debating whether we need to bring Robbo back as we now have a decent replacement!