[CMOTD]

I hadn't heard of the urethanes vs. rubber supposed incompatibility debate before.
Personally, I cannot see how one would affect the grip of the other, unless one was pulling "rubber" off the track, or the urethanes were leaving dust marbles behind
-  so again, thanks for being so thorough.

Not an uncommon debate over here. Complete nonsense in my opinion but some UK clubs ban urethanes over this alleged problem. Running both types together has never given me cause for concern on either my home track or the club one. Our local club runs an IROC class with handout Scalextric Ferrari F430s fitted with urethanes and virtually every other class has free choice of tyres (apart from silicone which does cause problems). The outright lap record was once broken by an NSR ultra clad GT immediately after a full race session with the urethane fitted club cars!

P.S. You have people using wintergreen on tyres? Really? Are they mad? It has been banned at UK clubs since God was a lad. The active ingredient is toxic and can be fatal.