Ahah it’s BLACK MAGIC! 
I turn off “divide shading subdivs”, so each AA step MULTIPLIES the base subdivisions.
In the case of the Archviz preset, the math is as follow (well, for how it shows up now. not user is identical to what i released, but the math is correct regardless):
8 subdivisions = 64 SPP.
(64 SPP * (4*4) (min AA squared) ) * 1.334 GSM * 0.75 (as adaptivity is 0.25, so 75% of the rays are cast regardless.) = 1024 SPP (and change).
Should the adaptive routines think more rays are needed, at the min AA level of 4 you’d get 1366 SPP.
Same applies for the Max AA, only in the forumla above 4*4 becomes 6*6, which leads to 2304 to 3073 SPP.
Let me know if i managed to get you more confused. ^^
Ah, and if you could show me what you mean (a crop is fine) about the fireflies in the GI, i may be able to understand where they come from: i definitely turn OFF max ray intensity, so that could be the case, if the HDRI is extremely bright in some areas. feel free to turn it back on by hand.