The phone's ROM was Bootleggers Oreo. Tested kernels: ROM's stock Derp+, Derp-v5.3, AGNi_PIE-v5.6, IceCold-R5.2, KangarooX-R4.4 and InsigniuX-x14.
This is by no means a comprehensive test (each kernel ran Antutu 7.2.2 only once), but is might serve as a starting point for some people. Before I attach the screenshots, I'd like to mention that IceCold boots the phone in less than half the time the others do, however apparently it was not enough to give it the crown (it's not overclocked). It also fails to show its information in "About phone", so I took it from termux.
All tests consumed 1-2% of battery and no tweak whatsoever was applied on the kernels (schedulers, clocks etc); they ran at stock settings.
I would like to thank the kernels developers for their hard work.
[EDIT] Added KangarooX-OC.
KangarooX 128,209 AGNi 125,286 IceCold 117,020 Derp-v5.3 113,870 Derp+ 113,597 InsigniuX 100,639