Just to inform you, it isn't double level to unlock Saibamen, Cell Jr and Cells Tournament. It's a set level you've gotta fight, and you've gotta be under that level. For Saibamen it's level 31-35. For Cells Tournament it's level 51-55 and for Cell Jr it's level 66-70.
I just unlocked Cells Tournament with a level 43 Vegeta against a level 53 Tien.