175mph, try 185/190mph on a good lap there.
If you really want to know the record around the 'ring is around 7min46 or so. I struggle to get under 9min30 at the moment but that time is improving.
One trick I have been told (from some one who has done under 8min in all cars, btw!!) and it seems to work, is treat the lap as a race distance on other tracks. Also go slower than you want to around the track, and only build up speed gradually. Try to learn the areas that you do not know, not learn the entire track.
If you want some help in setting the game up or just want to race quick try online racing.
www.vroc.net(or try
http://gplrank.schuerkamp.de/ for some more links) is the place to be, with on line races 24/7. here you can get links to alot of gpl stuff, like the add on tracks, (bathurst, lemans, etc) the upgrades to the game, etc. Hope this helps.