My comments are this are:
1. A neighbor of mine is a Dr and he said he sees patients with what we would consider low T but their mode, energy level, sex drive and performance is fine. Hence, hard to define a best range - very personal. I will give a number and say for your age, 500 to 800 though because I like numbers.
2. It is important to know that the labs set the ranges based on an average of the test results and I think that the ranges cover like 90 to 95% of people tested. So, IMO, the fact that the ranges are being adjusted down for T levels just reflects that on average people are having lower T values, but they may also be feeling like shit, so just being in range may put you feeling shitty like a bunch of other people. That is the biggest flaw in lab ranges that most people done understand. It just puts in in the herd, but a large percentage of the herd may be feeling bad and not healthy.