16 bit PCMCIA on PC has a max theorical transfer rate of 32 MB/s, on Amiga PCMCIA you get 3-5 MB/s if i remember well
Depends on what hardware you put there I guess, have not speed tested a CF or hard drive there but 3-5MB/s? seems fast, ive gotten about 400KB/s at most with peripherals added to the PCMCIA.