After having consistently measured 500-800 Kbytes / s on ftp
transfer with a 3C589C COMBO CABLE card I decided to check my
3CCFE575BT under Windows. The performance was just as under
linux, irregularly varying between 5 and 200 Kbytes / s
(mainly 10-20 Kbytes / s).
My conclusion is that the card is broken. Sorry for having posted this pseudo problem and many thanks to David Hinds for his continuous help !
best regards, Nicola