The roms would be fine on the SD card, in fact that would be my recommendation anyway as they are read only and are only read when launching a game. As for the poor performance point, yes i am referring to lag and slow loading elements in the UI. Launchbox/Bigbox is doing a lot of reading and writing at all times, its scanning image folders, scanning platform.xml's for game info, scanning for and playing videos, loading clear logos/boxart all at the same time, and SD cards really are not designed for that sort of random read and writes, they are more for steady reading and writing of single files like photos or video, or just general storage. My suggestion would be to keep the roms and videos on the SD card, but keep Launchbox and all the images on the internal drive.