Line voltage of 107 is uncommonly low. You might consider requesting your electric company check the transformer on the pole that serves you. My own experience with this is that the provider actually appreciates the opportunity to improve your service. Without your input, they have no apparatus in place to monitor the voltages in every neighborhood.
As far as your concerns about your amps' bias, my method, which is based not on expertise but on pure logic, is to bias your outputs when the line voltage is at its maximum (in my case the max is 118VAC, for example). Bias on my ST-120 can vary, but not by any great value. It may drop down to .50 at times (I use the standard of .55 recommended by Bob) but I know of no reason why a slightly LOW reading would cause any damage to anything. In short, I believe that once set under the greatest possible stress conditions, there should be no need to worry. Someone correct me if my logic is flawed, please.
I'm assuming that you are running KT-120s, since you are jacking up the bias to .60. Word has it that, even at this level, the tubes are not breathing heavily. What may be stressing is the rectifier. And I'm guessing that you use Weber SS units. Watch your temps on these. They are apparently fairly easy to melt down. But they are inexpensive. So keep an extra pair just in case (???).