This is hard to answer because you didn't indicate how much weight you will be vacation trips with. If you have an extra 30 to 40 pounds of gear, going up a steep climb of a mile or so, could really slow you down. Obviously, going down the other side would be easier from the "pedaling" standpoint, but can be dangerous if you get going too fast. You'll have plenty of "hills" to climb over there, that's for sure. There will likely be some stretches of territory where the 40 miles should be fairly easy, and may be completed in a few hours. Other times, if you have to climb 2 or 3 mountain passes in a day, that may take 8 hours or more. There should be some cycling chat rooms where you could talk with someone who has had a similar experience in Europe. You must know the terrain you'll be traveling through, as well as distance. 40 miles on fairly condo terrain should be a piece of cake, but 40 miles of gaining 12,000 or 15,000 feet of total altitude with a 30 degree ascent, may just be a bit tougher. You didn't mention any "rest days" for getting off of the bike, so you may need to adjust daily mileage for that or possible bicycle break downs. Hope everything goes okay and you enjoy the trip!