Stregadrea - we were very probably on that same Monte Carlo to Rome cruise with you, it was Sept 10-17 and I agree the weather couldn't have been better. However, we were on the sailing before, Dover to Monte Carlo, and as far as we were concerned the weather again couldn't have been better, we did have a sort or rainy day in Lisbon and light rain in Cadiz, but nothing that kept us from doing anything. There were only about 36 passengers that did Dover to Monte Carlo and then stayed on to Rome and I don't recall any of them saying the weather was horrible. Interesting.
Anyway, I have had clients sail that time of year and the reports are often mixed on the weather, guess its just like anywhere, as you said somewhat "luck of the draw". Good luck, hope its perfect weather for you.

We are doing Monte Carlo to Funchal and then the transatlantic in Nov of 2007 - now that should be interesting weather wise!