I have 2 WD MyPassPort. One 3to, the other 4to.
The 3to works fine, I mean as expected.
The 4to works but is very slow (under 30Mb/s).
My Passport are connected directly to my iMac.
I have also tried to switch both cables with no success
4to ref is
WDBYFT0040BRD-0A 0318B R/N:D8B EABEGA
Firmware : 4.004