I think that if you reduced to cruise at M0.77 your N1 would have been lower, then if you slowed to M0.76 it would have had to increase to counter the extra drag, more again at M0.75 and by the time you got to M0.74 most likely you wouldn't have had the thrust available to maintain the speed and commence even a 5 degree bank angle turn.
Do you think that the top of the amber band means you can cruise there and have 40 degrees of bank angle to the stick shaker or initial buffet? I'm assuming you know better than that but thought it worth asking seeing as the FCOM makes that statement.