How do the best centaurs compare to the best computers? Do human-machine combinations still beat the best computer chess players, or have computer players gotten good enough to beat even the best computer-human duos?
Two years ago, top GM Nakamura played a match against one of the top engines, Stockfish. In the first two games, he was assisted by a very strong engine, rating about 200 points lower than Stockfish. Still, this wasn't enough to win, he even lost this part of the match 1,5 - 0,5. More details, including games, can be found here.

Of course, a human assisting a computer player will be stronger than the same computer player alone, but this gives you an idea of how little we (human players) are able to add at the moment.