A couple of additional thoughts. Firstly as we all know the IMC rating is strictly only valid in the UK (although I have heard rumours yet to be confirmed that the Germans and French may take a different view). Therefore if you can operate on the N reg at least you can continue to fly in lower airspace in poorer conditions even if you are not able to operate airways because of lack of aircraft performance or of de/anti icing etc. Secondly there are those occasions in the UK where the flight can be executed more comfortably and safely in class A that would otherwise not be available.