K...I am trying to envision the folders. They sound very organized and awesome. But if I understand correctly, everyone has a folder? If you are partnering students, they should be sharing a folder. They take turns and after one minute they mark how far they go. Then each time they do the SuperSpeed letters, they try to beat their record. As far as partnering them up, you should have your strong students with your high-average students, and your average students with your low average students. That way the gap is not too big, as would be the case with high--low students.
Yes, your high students could "double" partner--but if you have students who already know the whole alphabet they may get frustrated with their partner if the student is too low. So same as the answer above--try to get someone that is not too far below their own academic level.
Hope that helps:)