using an 8gb samsung class 6 i think. waiting for a 32gb Transcend class 10 multirom!
probably, afaik i don't think class speed is that relevant when it comes to gateway/clone cards for the 3ds.
does having a higher class microsd card(class 4 vs class 10) increase the speed of gameplay, such as tempgba with pokemon fire red or catsfc with super mario allstars