Ok, I see a few items here that can make interpretation of your difficult.
Regarding drying, I am not sure how long you have dried the rolls. For PLA, I usually go for 6-8h at 55°C. Bambu’s recommendations are different but certainly err on the side of caution 
Only when the materials are known to definitely be dry can you really compare them.
But that does not neccessarily help with the tests themselfes. When scaling down and printing small parts, you can run into the minimum layer time. In the filaments cooling setting the 100% fan speed time criterion and a check box further down. Once you run into that, you no longer know which settings have actually been applied during the test print. The low angle at which you see overhang defects indicates to me that the test model did not have sufficient time to cool.
You can overcome this problem by printing 2 or more test models at the same time (far apart on the build plate) and/or forcing a prime tower by enabling it in"Other" settings and taking a “Smooth” timelapse.
As for that lower bound layer height, you can go lower than .08. But it’ll probably not help so much regarding overhang performance as flow control becomes an issue below .04mm.
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