If you test speed from the same location and using the same channels, and you repeatedly get the same results, then I would disagree with the <sigh> comment, I think your question is quite valid. I also disagree with the "Speed is not important! Connection quality is important.", because what is quality? Speed is measurable, and given the same speed, you usually approximately get the same quality (whatever that means) and pings. However, you cannot expect the same or better "quality" given the 50 Mbps+ difference in speed, its nonsense.
Regarding the reliability of the speed test. For example, on Speedtest.net, I constantly get the same results with a +-1% difference, at any time of the day or night, and we cannot assume that the Pavl's internet stability is different. So the "Many factors affect upload/download speed from the internet." comment is only partially true and may be not applicable to the current case, because even if this statement is true and Pavl anyway gets the same difference given the large number of tests, then, again, his question is valid.
AX82U can indeed perform better than AX86U, I've seen similar differences when comparing AX86U to AX58U and even to AX56U (when using 80MHz channels only). My impression is that the routers based on BCM675x system-on-a-chips are better performers in certain environments, maybe due to different hardware implementation or drivers, who knows.