I'm going to add to Rekstad's answer, because I think I see what you are confused about.
As far as I understand, in SuperSpeed Math, students set a goal the FIRST time they play, and after that, their goal is always set by their previous record....their goal is simply to break their previous best record. The first time they play, they have no previous record so they have to set a goal instead.
If you find that you'd like to make it harder or more customized for higher and lower students, you could have them set goals each time based on x-amount away from their previous goal, etc.... but in the rules of the game it simply says they are playing to beat their own personal best record.
As for SuperSpeed with a para (aide), I still think it's best that they take turns, because otherwise it takes away from some of the fun, silly, stumbling that happens in the game. If you read it yourself, you'll find there is a BIG difference if you read every word yourself, versus having to know when it's your turn and read the right words. It makes the game more challenging coordination-wise, and more fun I think.