I have found many forum threads discussing whether or not a faster SD card helps or not. From the casual testing people have done it doesn't matter much for 3ds games. However as the homebrew posibilites expand there may be usecases where a faster card may actually help out, because a homebrew isn't hardcoded to a certain speed limit as commercial games are. additionally it would be great to have such a tool to help figure out why some(or all) users are experiencing performance issues with cards larger than 32gb. Finally there could be a ram based test to figure out the theoretical maximum througput of the sd card controller.