I have read articles on both sides of the IAS and TAS issue; probably most were triggered when the RV article first appeared.  The accepted practice for certified aircraft seems to be IAS.

So, Vne issues asside, what say you about the prop speed issue?

I’d say keep the tips subsonic; beyond that your power is not producing speed anyway.  On my Catto prop (very similar to yours) the max rpm of 3000 is included on the label on the prop hub. Probably somewhat arbitrary, but keeps you comfortably below mach 1 tip speed.

Al