The speed settings are actually settings to slow down the response from the joystick ports, for games that use speed-sensitive code to read the joystick. Any game that was programmed properly (most coders had figured out the correct way to read the joystick by around 1990) will work fine no matter what the gameport speed setting is. Any speed setting should be fine in your system for most games you'd want to run.
Put another way: If there is a game with bad joystick code that fails on your system, chances are very high the game itself runs way too fast as well and would be unplayable even if the joystick were completely functional. (Think about games made before 1984, where they were hard-coded to a 4.77 MHz 8088's speed.)