A few thoughts:
* I would use more modest increases in speed when you near AeT during your test. For example, it would be good to know what your readings would be at ~168 and ~178. Increases of 0.25 mph may do that.
* Correct, the definitions of different zone systems are less important than knowing the key inflection points of AeT and AnT. In the simplest terms, you could say that there are just three zones: below AeT, above AnT, and between the two.
* The closer you can train to AeT (~173 for you), the more aerobic the training effect you’ll get. However, the desire to do so has to be tempered with the fatigue that that training creates. As the gap between AeT and AnT narrows, the metabolic cost of AeT work remains low, but fatigue from that work increases. So an athlete that may have been able to put in hours at AeT in one session when beginning training will need to eventually back off. Future AeT work will be reduced to minutes, and likely done in an interval format, as the athlete becomes fitter. In addition, recovery paces will likely become slower to offset the increased intensity.
* Training Peaks actually works pretty well for measuring this type of fatigue because it ignores AeT. All TP calculations are done off of AnT, so as AeT increases, TP calculates higher amounts of TSS accordingly.
I hope that helps.