I think the fastest I went in any car, Boxster incl, is 160km/hrs. Cars are way way way too heavy for me to be able to handle if anything goes completely wrong. Actually scares the hell out of me.
However I have a 210hp superbike (Honda HRC Fireblade or CBR1000RR) and track/clock this bad boy at over 312km/hrs on the back straight twice every single months
Below goes fast! Boxster = showoff at traffic lights only