I do have the speed test disable box unticked, yea. Good call on the 'always on' setting, that seemed to have fixed my bufferbloat. Seems like I must have had something open in the background during my previous tests that was causing the router to use congestion control while I was running them.
Will update to 4.0.41 again later to confirm that fully fixed the problem.
Now if only I could figure out why my ping was 10ms lower the night after I went from 4.0.21 -> 4.0.23 and if it's possible to get that low ping back.