I redid my kickr power test after putting on 3 new chains.
with three old chains, measuring between 1.4 and 1.6mm stretch over 8 links (double the recommended replacement amount. oops)
Kickr | Argon | Foil | Speen Concept = 237 | 250 | 247 | 243
with new kmc chains all measuring 0.00 or 0.01 stretch.
Kickr | Argon | Foil | Speen Concept = 237 | 246 | 245 | 244
So 4 watts on the argon chain, 2 on the foil, and +1 watt on the Speed Concept. Given the kickr measuring at the wheel and the rest measuring at the crank, I'm pretty happy with those numbers and their consistency.
Some of it is just noise, too. The kickr shows 237 flat, all the time. Up down no more than 1 watt, but as cadence goes up and down the cranks reflect the increasing and decreasing power as the kickr adjusts. Regardless, nothing is perfect but I'm happy to have done it, and now I'll try to be good and change my chains on time. 4 watts counts!