You have asked the question every traveler wishes he/she had the definitive answer to!

In my experience, buying now for a May trip would be too early unless they were ridiculously cheap. It's unpredictable, what prices may do, but I'd certainly wait til at least after the holidays.

If it was me, I'd get serious about looking about 8 weeks before and then snag the best fare. My daughter bought her tix to Europe this Past May about a month before her trip and got an excellent fare.

I would start watching fares now and be ready to jump on a sale. You can sign up for fare alerts on a couple of sites. I use itasoftware.com to search flights (they are the company that runs the programming of many commercial sites). You can't buy on their website. You have to go to the airline and book after you find your flight.

Some flights to Pisa are seasonal and won't be running in May.

I think only Milan and Rome have regularly scheduled flights landing from the states. Venice may have a few and Pisa has mostly seasonal. Florence and Bologna require changing planes in Europe somewhere as does Naples. Is Milan close to your final villa? Are you renting cars?

i posted the same type of question here last summer and people thought the fare i was looking at was a good one-- of course, 5 days later, it dropped by $300. you just never, never know.

i will say that, after the price drop, i sent a letter to my airline (united) saying that i felt they were manipulating fares to scare people into buying. (they dropped and then raised and then dropped the fare the week before i bought... so i bought when they dropped... but then they seriously dropped.)

they actually contacted me and told me that they will give you the lower price (with a $75 fee)... which i had NO idea about. this was not a refundable ticket, and i had not purchased their fare guarantee add-on. so i did pay the $75 and saved $250 over my original price. just fyi.

thanks for responses. picking up a car in naples and then dropping it at departing airport. milan is a couple of hours drive from our northern tuscany villa. have found several 1 stop flights from florence or bologna via air france. milan fights seem similar but a little more expensive.

Kayak, with the billions of flight searches on their site, did some data mining on this issue. For international flights, 34 days prior to departure seems to be the sweet spot.
http://www.huffingtonpost.com/2012/10/18/the-best-time-to-book-airfare_n_1978346.html

Yup - three to four weeks before the flight, and buy on a Tuesday after 3 pm EST, according to the World Bank Credit Union newsletter this month.

how much of a savings by waiting? 10%? 20%? for $200 or so, i wouldn't want to risk paying $500-700 more if flights fill.

thanks

also don't want to get a cheap 20 hour/3 stop flight just to save 10%.

Then just buy when you're comfortable with the price. It's always a crapshoot; there are never any guarantees.

>>>they actually contacted me and told me that they will give you the lower price (with a $75 fee)... <<<

Most airlines charge $250 to change an international flight ticket if there is a price change. Here's a chart (not sure it's up to date) showing what the various airlines charge in price drop situations.
http://www.airfarewatchdog.com/blog/8468624/chart-airline-fare-drop-refund-policies/