I have a 2008 M3.
Just before I put it away for winter, It had 99,600 km (almost 60k miles)
longest trip was 3200 KM. They're great on the highway. Mine is an E92, I flew my wife/kids out so I can drive alone on the way there. We drove on the way back. Kids had no problems with the carseats (5yr old and 1 yr old)
my only issue is.. my comfort access doesnt work. knock on wood, everything else has been great.