First of all, these cars do not like accelerating from low speed. You have to ease into the throttle instead of hammering it. There are several things that can improve this:

More rear wing
No Auto-Clutch
Use traction control
Faster pace laps

I can edit the track files to make the pace laps go faster, but there is one key problem with that, the faster the pace car goes, the harder it is for the leader to catch up to it at the start of the race. It's a catch 22.

Other than that, the cars do seem pretty stable.