I race with RPE, occasionally looking at my heart rate to see if my heart rate matches how I feel. Sometimes I use that as a “I’m not pushing as hard as I thought” (when I sitting at like 150) or on other times “Ok, I guess I am going hard” when I’m seeing 170’s. But it’s still mostly just perceived effort.
I did a race recently where the start was at about 8000’. Power numbers there are meaningless when I train at sea level. After the race was over, even though I had a good race, looked like a relaxing day.