You are right, you could never reach 100MBit with the Thylacine. I have one with a 10Mbit adaptor in my Amiga 4000 and can only get around 50Kb per sec max to my LAN so the 100Mbit adaptor would probably only manage the same with the Thylacine.
Oli_hd is also correct in assuming the card is not Zorro III, it is only Zorro II and the Cypress SL811HS chipset it uses has only an 8 Bit interface so it is only using half the width of the Zorro II bus. You could never expect great performance of these devices with classic hardware, USB is very demanding of the system. It's still good though to be able to access these devices with classic Amiga's.
The main reason these drivers were probably written is because the Thylacine card uses 68k versions of the AmigaOS 4.0 USB stack software which means these drivers could also be used with the AmigaONE's USB ports.
