Thanks for that Wapping, I take it from that diatribe that perhaps like me you have never been there, so can't offer anything useful. Not all of this parish are riding up and down unmade roads all day, or being what is called 'adventure riders'. I just happen to own a BMW GS, because it happens to be a damn good bike and I go touring because I have a physical handicap that prevents me from doing otherwise.
I am not sure you actually read it all, nor took in that I sympathised with your 'lLong days in the sadde' concern. Try reading it again.
No? Still no good?
All right. Here is the very brief version:
Ask the organiser where (and down what type of roads) he intends to ride for nine hours in the saddle for two hundred miles each day. We have no idea, nor can we guess what he means by nine hours in the sadde to go 200 miles any more than you can. In short: ask him, he knows.
Moving on. Me, as a bod who doesn't ride an 'adventure' motorcycle (so you are one step ahead already) or go up and down unmade roads all day in the heroic style, preferring to simply 'tour', I can (with absolute certainty) tell you that most of the roads are fine. Some perfect, some middleish, some less so. If you are happy with that (and think you can manage whatever the bod tells you he is planning to do) your next nine months will fly by. I hope they do. Let us know.
PS See this post for what I think is a reasonable rule of thumb on what a (non-Adventure) on-road-tour (on half sensible roads) involves:
http://www.ukgser.com/forums/showpost.php?p=3299499&postcount=6
It comes from this thread: http://www.ukgser.com/forums/showthread.php?t=322434
Not the same part of Europe as you maybe plan on going, but the underlying intent is much the same. If you like, take of 50 miles from the 250, simply as it's the eastern side of Europe (and because you can) which will leave a reasonably comfortable (for me at least) 200 miles in a sensible day. It may not work for you.