I've had 5 sets of Pirelli tires over the last 20 years. Mileage is excellent - always 60-70k kms every time. Got my present car (z4) with P zero nero runflats fitted - did 65,000kms on them. Replaced with zero nero standards - as you'd expect, the ride is less harsh with the softer walls, but I'm very happy with the overall performance.
My experience is that Michelin's will give you an extra 8000 - 10,000 kms but Pirelli's are significantly quieter.