GPIB-USB > NI 120A ?

1.

Can still use 28 ( 2 x 14 )  devices if I'll use my NI 120-A GPIB extender/isolator with a NI GPIB USB converter ? ( Instead of max 14 devices of the NI GPIB USB converter itself  ?

2.

What is the difference between GPIB-USB B and HS ? ( different speeds .. ?  if so what speeds ? )

Thanks,

Peter PE1E.