I've actually gone back to heart rate. Still use power to monitor progress
The big four types of data to capture and track:
RPE + ROF - How hard was that, how do I feel today
HR + HRV - How are you responding to volume and intensity
Power - How much work did you do, How hard was it
Course/Distance + Time/Speed - The ultimate integrated measure of performance.
All four types of metrics are vital - and have the added benefit of being concrete, individualised and largely repeatable and reliable.