Actually I did tons of test with DSLReports speed test. I tried different variations (with ntce enabled, disabled, only IntelliQoS enabled, only priority 1-2-3-...-6 for testing device connected with Cat6, IntelliQoS enabled + priorities and much more)
My ISP provides 100 Mbps for me but since it's fast ethernet I can only reach 95 Mbps which is fine for me. After tons and tons of testing (as you can see) I think my best bet is disabling every setting (therefore no IntelliQoS and default priorities).
Default settings (no speed limit, no IntelliQoS, default priorities)
I tried IntelliQoS and changing priorities but they were ineffective, gave me similar results.
I got best results with limiting speed only (like 94000/8000 kbps, no IntelliQoS, default priorities) so I wildly guess that speed limiting somehow enables queue management.
I don't say these results are bad. It is fine actually. But my older garbage tier ISP modem did it better without any config (no tests since I don't own it anymore) so I expect that Keenetic can do it much better.