Just wanted to add something to the discussion...
Turning two ADRs would force the a/c into alternate law, as would turning the two FACs off.
Considering it is the FACs that determine the speed protections surely it would be more sensible to turn these off rather than the ADRs and leave yourself with only one reference for airspeed info.
With the FACs turned off you would only lose your high and low speed protections which is a better place to be in than losing your actual airspeed? Of course you would lose yaw damping etc. but I would still consider this to be better than losing two air data units.
Please correct me if I am wrong
Cheers.