Paul,
My 166 3.0 was coming up to similar mileage and age and the catastrophic implosion of my friend's 166 2.5 at five years and 55,000 miles caused me to consider this question very carefully.
I read all the horror stories here and spoke to Ramponis and they suggested four years or 48,000 miles. In the end I chickened out and had the belt changed last month at nearly four years and 37,000 miles. I didn't want to risk waiting for 48k.
FYI: belt, tensioner, all the bits, new plugs, annual service, came to EUR 1,100 - I had it done in France (main dealer).
Michael
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