I've taken a VFR from London to Slovakia. Going through France, Belgium (for croissant breakfast), Germany (Overnight stay in Boppard - Fantastic place, plenty of wine), on through Bavaria (Overnight stay in Augsberg) and then back up to the autobahn at Regenburg, through Austria (stay the night in St Poellten) and then arrive in Poprad Slovakia by lunchtime on the 4th day.
Maximum riding time each day would be around 6 hours, plenty of petrol and food/drink stops and not one day leaving before 9am (except the first day).
Had a totally brillaint time - the roads in Germany are unbeatable. Flat, smooth, twisty and plenty of vision. I wouldn't say it was the best route because I had a deadline and visited friends in Augsberg. A trip around Germany and Austria only would be awesome.