I’m no expert on this stuff so I will only share my opinion and experience.
If I were prepping for a race I would consult the charts; otherwise just go with RPE. If you are training with power the Garmin app will incorporate wind if you carry your phone on runs (I haven’t tried it but it, perhaps someone else has some practical experience with the technology).
I have always lived a about 300 ft. When I have traveled to 5000 ft I experience a definite slowdown when running, below that not a significant impact.
I did the Mt. Whitney day hike from Whitney Portal (22mi RT, 8000-14500 ft), and even after three days prep hiking at 10000 ft I was sucking air. That’s an extreme, at 3000 ft you should be fully acclimated after a day or two, but that is only based on my particular experience and I don’t handle elevation all that well…