I believe it would be 0.2g to 1.8g. To be honest it may be simpler to just make the game, go to race details window (ctrl+F2) and change gravity tolerance there, as it uses not percentages, but absolute values. You can do that at any time with SM mode, even if you already established colonies on planets that will no longer be habitable. Of course if you do that you'll end with a lot of dead people, so no exploits there.