Yeah the biggest aspect sims are helpful on is learning tracks....
in 2006 when I did FIA GT3 at Mugello, learning the track on GTL (at the time) must have saved me about 10-15 laps (30 odd minutes). After a few laps i was already doing decent times
Also GTR2/rFactor are so in-depth with car settings, there are more options than on most race cars in real life! So it helps you learn the concepts.
As far as handling goes i've never driven a GT1 car but they aren't much slower than my group C car, although 150-200 bhp less they obviously have sequential gearboxes and better handling while for me the gear change and turbo lag is sometimes painful!
But like the group C car you can feel the sensation of aerodynamics working on the GT1s on the game esp. during high speed corners.
As far as GT2 goes i've driven a 996 RSR and RS and feel the game models a 911's characteristics quite accurately. The problem with a game is you can only judge what the car is doing through the steering wheel and exaggerated tyre squeal sounds
and in the real life you feel it mainly through your arse
The 977 GT3 Cup Car mod for rFactor is one of the realistic but that is a car i've driven the most in real-life and the mod was co-developed with a team and driver in the Carrera Cup...but very impressive
I just wish GTR2 modelled some more realistic aspects of a proper race. For example with most cars having carbon fibre bumpers etc punctures are more frequent after collisions with lots of debris. Also fluid from cars is often a problem, in 2006 when we were racing in Carrera Cup at Silverstone National, there was first corner contact and coolant was dropped on the apex of Copse. So for the whole 25 min race (not long but tyres went off after 15 mins!) people were hitting and spinning and going off etc, but most drove a wider line etc. (the sensible thing to do!) but the spectators loved it sitting on the first corner waiting for someone to crash
Further to that, fluid should definitely include oil. Cars as old as the ones in GTL tend to leak quite a bit and sometimes when testing with them it's not uncommon for them to drive most of the track (on the racing line!) dripping oil !!!
