I'm not anywhere near the speed of the GPLaholics around here, but I can
manage a 1:12 at the Glen in the Ferrari, so I guess I can attempt to
give you some advice (and hopefully not mislead you too much :o) ). My
advice is to watch the replay that comes with the game. Also download
Huttu's if you can find them (sorry, too lazy to look up the link right
now). This will show you the most important things, which are firstly
the line, and secondly the markers for braking and for getting back on
the throttle (crucial!). Also save some of your laps and compare them
to better drivers using GPL Replay (again too lazy to look up the link,
hehe). In particular, I think the line through the esses is critical
because it determines how fast you are going to get down the longest
straight. As for the 90, the best I can do is just drift through it
sideways in first. If you're unstable in braking it might be due to
engine braking - try either downshifting later or blipping the throttle
when you downshift. There - now hopefully somebody with more experience
than me (i.e. just about anybody) will jump in and tell you the right
way to do it. ;o)
Good luck,
Haqsau