Hi Larry

My understanding is that ACEA A5 has the same wear performance limits as A3, so there is no advantage in moving on this basis.

A5 does have fuel economy criteria, which means that oils with this performance level will be formulated differently and also means that thicker oils (eg a 10w40) are excluded  from being labelled A5. 

Given the above, I do not see an advantage in moving  to a A3 rated oil, if you continue to use the same oil grade (eg 5W30).

ACEA C3 is a different style of oil, formulated to be low ash, typically for use in vehicles with DPF's. 

I will also add that  if the vehicle is in warranty, that only the oil peformance level nominated by the warraty provider should be used. 

Cheers

Costa

Penrite