RE: Sardinia in May?
I spent one whole year in Northern Sardinia during military duty. It was back in 1988 and I was in Maddalena, close to Porto Pollo where I sailed every time I was able to (about 100 days on the water that year).
I remember the wind being there for long stretches of time, then off for other long stretches of time. More or less, it was 1 month on, 1 month off. I got consistent nice winds in May and July. I remember my parents were telling me that in May it was raining almost every day in Rome... but it was sunny, warm and 20 knots almost every day in Porto Pollo. In August, it was windy almost every day, but lighter. Winter months it was no wind at all, or 40 to 50 knots.
May is not vacation time in Italy, so you will not find it too crowded; he place is fantastic; the air in May is full of scents. A delight even if one does not sail. Go there.