Your pennies taken and I'm broke so I'll keep em.
I own an EVO X (2010) and this generation is the first in the US with what you refer to as the diff sending power to the outside wheel is called AYC (auto yaw control). It is a hydraulic pump that sends power to the outside rear wheel only (not front, that remains a more conventional LSD). It can be felt on the road AND in the game but it requires (in real life and in GT5) a slow in, fast out approach to driving. Going to fast into the corner will still result in understeer but if you approach the corner at a slightly slower speed, the AYC helps you power out with a neutral attitude. I wouldn't call it oversteer, but awkward if you've never experienced it. Just,...turning.
All EVO X's also have AWC which is a computer controlled central diff that will let the front and rear axles rotate at different speeds. A lot of people mistake it for "sending more power to the rear wheels" which to my understanding isn't true. It let's the rear in Tarmac mode slip more than the fronts which will help with rotation. Likewise, snow mode is a tighter setting that let's the car have more a locked diff btwn the two different axles (f/r). I just have to assume they set it to default to Tarmac mode in GT5.
The EVO X also has a neat trick of being able to brake individual wheels into a corner to inhibit better turn in. This is the feature I don't feel in GT5 that exists in real life.
I used to also own an 08 STi which also feels fairly accurate in GT5. More meaty power wise but pushes a bit more in the corners. A little less corner entry understeer, but you have to wait a bit longer to get on the power.
Hope it helps.
