No your not mad at all. Cycling is a great way to travel around europe. Last summer i cycled from northern france to Oslo in norway (about 1100 miles) and its one of the best things ive done. Im currently planning a 4000 mile cycle from calais to the ukraine via italy, greece and romania. Im just guessing but i recon paris to istanbul would be something like 1600 miles depending on your route. if your fit you could do that in 18 days but you wouldnt get to see much. the great thing is that you can take as long as you like and go where ever you want. if you were trying to see as much of europe as possible id recommend taking a 2 months or more to do it. 40 miles a day is easy and would only take about 4 hours/day. go for it, but plan it properly because you dont want to find yourself in germany with your plane leaving in 48 hours.