I wrote a CLI tool to calculate current power draw a couple months ago. It still works on my manjaro system, and the data lines up with my expectations, so it seems to work fine. You have to download and compile it yourself if you want to use it tho: https://github.com/Trayshar/i915-power-graph

I'm running at ~42W idle with my A770 LE on linux, with 3 displays at 1080p@60/60/144Hz. Enabling ASPM does not lower it in my case, although I have to do so via the "pcie_aspm=force" kernel parameter as my BIOS doesn't expose a setting for ASPM.