Hikaru Nakamura became the first U.S. chess player to reach a score in world rankings of 2800. He also is leading the Zurich Chess Challenge after round four. Former Champ Gary Kasparov was the only chess player to retire at a 2800 score. Topolov could have retired at 2800 yet has decided to play on-a good thing since he and Boris Gelfand are the two Mikhail Tal style active players (interesting attacking play).
Bobby Fischer had a ranking in a somewhat different system. Various computations find that he reached 2900 in his best year. He retired with the highest winning percentage at 70%. Kasporov retired with a 69% score in a tough era too. World Champion Magnus Carlsen reached 2880 on his way to taking the title, yet fell short of 2900. One hopes that he becomes the first player to reach a solid and sustainable 2900 score for a year or two at least in order to clarify the issue.
Nakamura is also hoping to qualify for the candidates tournament next year and have a shot at chalenging for the world title.