Something to keep in mind is accommodation.

When we cycled northward up the west coast of France on the Velodyssey Route at the end of September 2012, we discovered that a lot of campgrounds, hotels, etc. closed at the end of September. It became rather challenging in a couple places to find accommodation that was open.

Also August is a big tourist/travel month. We were doing the Rhine Route in August 2012 and the challenge there was finding a place with space for a small tent ... many of the campgrounds were full. Other less popular parts of Europe would have likely been a better choice for August.

Before you make a firm decision, you might want to check what time of year the campgrounds close in the area you want to travel. Depending where you go, you might be all right, but it is good to have an idea about that in advance.