When I went from 15inch to 215/40/17 on my Alfa 75 3 litre I found that dropping the pressures by about 2lb all round from the handbook recommendation made a better ride and handling (28lbs all round). The tyres still wear perfectly even, P7000's and I swear by them.
Just try different pressures until you find something that suits you, and the roads that you have to drive on.
The pressures quoted in the handbook sound excessive, however the new GTV I had was quoted at 37lb for the fronts, so you never know, plus modern cars are getting heavier all the time. The 155 is lots heavier than the 75, and the GTV is even heavier again. I dont like the ride on my 155 sportpack and I am going to drop the pressures on this to see how it changes things....