I had an amazing 2.5 month ride around Europe this summer on my Pan European, I wouldn't even dream of driving it.
Far too many road works, crashes, narrow roads and passes meaning car drivers spend most of their time doing nothing. I [size=78%]think you'll find it very frustrating doing it in car, especially if you go anywhere near tourist areas.[/size]
If you do make it to the more eastern countries, remember to get a vignette, needed for the motorways.
The roads are far better over there, and even the petrol is cheaper and higher rated that our stuff (I was using shell race fuel sold at most of their garages - 106 RON, for under 80 pence a litre).
I wouldn't bother with the Stelvio pass in Italy either, completely overrated as a driving/riding road... the route heading south into Bornio is far better (IMO)
Southern Germany has some great roads, as does Southern France into Spain. The route around Italy into Monaco etc is very nice, but again it's really jam packed with cars at a standstill in all the small villages etc.