No major opinions either way on the Bridgestones. The biggest issue was with them being low-profile runflats, meaning they were not particularly comfortable (especially with the pretty firm suspension on the Z4!) and caused a crack in one of the front alloys.
The rears are completely shot after 10,000 miles, but are dealing with over 300bhp, a fair bit of camber, and some ocassionally "boisterous" B-road driving, so haven't done too badly really. The fronts have still got a good few thousand miles left on them.
The dry grip was pretty good, but not especially progressive. They gripped well up to a point, then just seemed to let go, but did come back into line reasonably easily in fairness.
I wouldn't buy them again purely because I think there are better tyres out there for the money. I'm replacing the back 2 with a pair of Hankook k107's so we'll see how they compare...