Hi there,
My first posting, I couldn`t resist any longer....
At our airline we fly both the -400 and -300 in the EFIS style. We have no ASI`s, other then tapes and the standby. The standby is the cheap drum-type, with its own ports.
The tapes get their speed info from their respective Air Data Computers. The input from the FMC to these tapes is of minor importance; upper and lower yellow bands.
We have captains EFIS on standby-power for a minimum of 30 min.
Regards