So which out of the stages and 4iiii is closest to the power reported by the wahoo kickr?
You can experiment by simultaneously recording the wahoo kickr and PM power on separate devices.
If you do compare the PM and the kikr this is a free comparison tool that I stumbled across
I have done extensive testing/comparing my power meters (Quarq) relative to my Kickr Core. The Kickr is remarkably consistent to with +/- 0.5 of a watt over dozens of workouts at various power zones. So I use the Kickr as the “control variable” to compare all my other power meters that are on my trainer bike, gravel bike and MTB (which all have separate Quarq power meters). The Quarq is slightly more variable up to 3 watts when compared to itself, however still within +/- 1%.
Even amongst the same power brand, there are some differences. However, I’m able to adjust the Slope of the power meter on the Quarq so they all now match +/- 1.0% (this was the advice from the manufacturer SRAM after sending them all my data/tests). The Quarqs weren’t horribly off to begin with but enough to throw off some zones and load/TSS.
Im not sure if other power meters have the ability to adjust the Slope, but this has been great to align all my power.
Then I wouldn’t put too much faith in the numbers. The differences can easily come from changes in left/right balance.