I plan usually not more than 300km a day. That way you can explore also smaller roads and don't rush to keep up with your schedule. Some day you will probably cover twice as much, but other day you may be struck somewhere for whatever reason.
I can not suggest any specific place in Europe - just don't plan too much for one trip if you are not just collecting places in style "I have been there". Pick one region at a time and spend more time with locals - you will discover much more than just rushing through countries.