Fastest I've ever been for a small amount of time was around 200/210 km/h (by tach) on an Alfa 156 on an italian highway (we were 8 or 9 cars coming back from Varano de Melegari).
I sometimes hurry (if needed) around 160/170 on some very long, straight and desert bulgarian roads.

The fastest car I've ever driven (albeit just manouvering, sadly) was the speed world-breaking record Alfa 155 Q4 which you can see in this page:
http://www.alfaclub.lu/HTML/know-content.htm
And which is now on display on a Alfa dealer in Legnano (milano), Italy, where I've worked for a couple of years.
You'd need a crane to get into and the b@tch dies below 3k rpm ... but she has an amazing roar!!