estrick: Fischer's 5th move is the most common in the CG database, and scores reasonably well with 38.7% wins vs. 22% losses, with 39.2% of the games drawn.
The second most commonly played move, 5. 0-0 scores better with 42.8% wins vs. 21.2% losses.
At a depth of 18 ply, Fritz seems to think that 5. d4 is best with a +.48 evaluation. 5. c3 is Fritz's fifth choice with an eval of +.20
Fischer played this move on two other occasions and won both games. However, the move seems to have disappeared from top level play over the past 30-40 years.
7. 0-0 seems to have been the most commonly played move in this variation.
Fritz rates 7. Be3 and 7. d5 as the best moves here. In recent years both moves have been played and White has scored very well in those games.
There are only ten examples of this move in the CGdb. White has 3 wins, 4 losses and 3 draws, -not great.
In his game with Olafsson at the Candidates tournament a few months later, Fischer played 8. Nbd2 and won in 78 moves.
Fischer vs F Olafsson, 1959
Three years later, against a lesser opponent, Fisher tried 8. Qe2 and won in 26 moves.
Fischer vs V Ciocaltea, 1962
Fritz rates 8. Be3 as slightly better tha 0-0. There are five examples of this in the CGdb with White winning 3 and drawing 2. But none have been played since 1955.
After 9. Nbd2 Be7, there are nine examples in the CGdb, and White is winless in all games, with four losses and three draws.
At 18 ply, Fritz rates 9. d5 as best with a +.43 evaluation. Strangely, this has not been tried over the board in master play. At least there are no recorded examples of it being played in the CGdb.
There is still room for innovation in opening theory!
At 19 ply, Fritz rates 9. Be3 at +.45. This was played once in 1923 and again in 1955. Black won once and drew once.
9. Nbd2 is only rated tenth best by Fritz, with an evaluation of +.23
Fritz seems to like this move the best.
By transposition of move order, there are twelve games in the CGdb that reach this position. But after 10. ...Bg5, 11. Ne3 Bxe3, Black wins five of the games and draws six, with White winning none.