I've had a couple of 911 (997) GT3 RS's and an R8 at work, but they were only just moved around, not taken out on the road...

Probably the quickest/most powerful thing I've driven on the road was a 380/400hp Supra, I picked up for a customer, took it to work (12miles) and then back again. Got on the motorway doing 40, nailed it, within literally seconds it was doing 140, lost my bottle with it at 155 (GPS indicated)

Most expensive ever driven was a McLaren SLR - but like the GT3 RS's and R8, I only drove it about 0.2 of a mile