The same SD Host Controller is in the FT93x and FT90x. Our measured speeds are (Class10, 16KB Cluster, FAT32): FT930, SDCLK@25MHz USB Read (100MB): 9.7 MBytes/sec USB Write (100MB): 6.8 MBytes/sec FT930, SDCLK@50MHz, Class10 USB Read (100MB): 18.5 MBytes/sec USB Write (100MB): 8.0 MBytes/sec.