Hi Juan,
I feel proud to share this thread with you bcoz i became fan of you by reading your articles 
As per my knowledge,
The user's who logged in AS (City B) will feel the poor performance when they do the operations like Insert, Delete and Update bcoz the data needs to updated/deleted in the Database of the server which is in City A.
And you mentioned that adding one more AS in the same city B, Will definitely helps to avoid downtime(if one is unavailable) but may not help by means of performance as both are in same city B. Network is same so that Performance also same for one server or more.
These are my views/opinions and correct me if m wrong....
Regards
Santosh K