I finally had some time to measure the static deflection of a hard axle (OTK H) and soft axle (OTK Q). I used 20 lbs of weight on a bar that extended 22" past the end of the axle to provide additional bending load.
Axle test rig.
This is the H axle deflection.
This is the Q Axle deflection
They both deflected the same, .015".
The only problem is you’ll have to trust me that I didn’t fake the results.
I’m in the camp that axle hardness/softness makes a difference both in feel of the kart and lap time.