This is a very personal question, but I just blurt it out. You don’t want to run low, this is just ugly and potentially deadly. I actually do everything to avoid the lows and will take some higher numbers in exchange.
For all practical purposes I set the lower range at 60 and the upper at 180. My A1C’s run anywhere from 5.5 - 6.1 with a TiR of 85%, above 180 10% and below 60 about 5% with an average deviation of 45.
That deviation is the number I believe is actually the most important. If your deviation is very small even though you run higher readings but you are constantly within a deviation of 20 between 140-160, you might be better off than with a deviation of 40 between 80-120 readings which should be the ideal numbers? I leave that to the real experts to chime in on that?
I don’t believe that you will mess anything up if you even run occasionally higher than that but maybe your Endos patience with you. I am a T1 for 30years now and maybe the last 10 years I control the numbers a bit tighter since I can with all new tools available. But I was absolutely not letting diabetes control my life and my work but tried to control it just as much that it would not bother me with any side-effects. In numbers that probably means A1C’s above 6.5 - 7 at badly controlled times and accepting the 240 plus readings. Gladly enough it has not shown any ugly long-term effects with me so far. But everyone is different, that is why it is such a personal question.