M4 is rapid (as we all know). However, on a public road, M4 v RCF / GSF, I can’t see there being a winner (other than the law). Given your average driver, in the wet, I honestly don’t think an M4 would know which way an RCF / GSF went.
I’m not a capable driver, but what impressed me most about the RCF was the wet weather handling. Never once did my car (unexpectedly) break traction. I was told by another driver that TVD does allow some tail happy behaviour in the wet.
ISF / GSF / RCF straight line performance, not much in it (as you would expect).