120 ( +1 | -1 ) Depends on the GM!!1. Depends on whether the GM is FIDE or ICCF--some FIDE GM's (e.g. Ulf Anderssen) are excellent correspondence chessplayers, but others aren't. 2. Within those ranks, there is also a wide disparity of age, skill, etc.--some GM's are old and/or out of practice or were marginal to begin with while others are killers. 3. As many times noted in these pages, every Elo rating system is CLOSED and ratings are therefore relative only to the group of players within it. Hence, one cannot project a rating for an "outsider" except by their relative ability to some players WITHIN the group who also play in an OUTSIDE group 4. Therefore, one would look at players such as Rodog (Senior IM in ICCF) and Cairo (several norms towards IM and SIM in ICCF) and conclude that a ICCF GM with a 2600 ICCF rating would PROBABLY eventually earn a similar over-2600 rating on GK given that Rodog is over 2500 in both systems and Cairo over 2500 in both systems. But nothing is certain, given that a player would need to adjust to the differences between GK time controls, vacation rules, etc., and those used in ICCF play.