@Tony:
I run a thorough test and here are the results achieved during the qualifying session. For comparison I also post my fastest laptimes. They are not perfect but good - laps without grave mistakes. I also paid attention to the top speeds and gears at the end of the s/f straigth (before Senna-S).
Track: Interlagos 1995 (by Fongu)
Driver(physics): Schumacher/Benetton
my fastest time: TC on - 1:21.0xx - 5th gear - 272 km/h
pole position: Hill - 1:18.0xx
Driver(physics): Coulthard/Williams
my fastest time: TC on - 1:15.5xx - 6th gear - 292 km/h
pole position: Hill - 1:14.7xx - Schumacher: 6th gear - 294 km/h
Driver(physics): Alesi/Ferrari
my fastest time: TC on - 1:21.0xx - 5th gear - 273 km/h
pole position: Hill - 1:17.9xx - Schumacher: 5th gear - 277 km/h
Driver(physics): Chiattarella/Simtek
my fastest time: TC on - 1:18.7xx - 280 km/h
TC off - 1:17.4xx - 280 km/h
pole position: Hill - 1:15.0xx - 6th gear - 295 km/h
To sum up, here my impressions:
There are two different types of physics.
1) The first ones (Schumacher, Alesi) are relaitic concerning laptimes - the cars have only 5 gears and a top speed of approx. 275 km/h (concerning Interlagos).
I don't like them because they cause huge understeering - I am always faster when I turn off TC because this way I can direct the car to the apex by sliding. The Benetton (TC enabled - but also with TC off) is very very stable to drive - but understeers extremely so that I am 3 seconds slower than the Williams.
2) The seconds type of physics (Coulthard, Chiattarella) are very nice - but the cars are much too fast (1.15.xxx). There are 6 gears and the top speed is 290-295 km/h. The cars are a bit nevous even with TC, but this way you can drive faster because there is no extreme understeering.
Imo the best combination would be physics 2 with performance values of physics 1.
The best result has been achived when chossing Coulthard (+0.8 sec). If I develope a setup adjusted to my driving style I can go for pole - so that is realistic and challenging.
I only tested these four teams. I assume there are also these differences for the other teams.
Btw, one problem I also have is that the onboard options (fuel, tyres, leave the pits) are not fully displayed - they are a bit too far on the left side.
Well, that were my impressions. Does anyone else encounter this, too?