I don't use the GS to beat the game. If I'm impossibly stuck and will never pass it, I will shark it through but I got the shark to do things with the game that couldn't be done otherwise. 2nd player autopilot is one(since I'm so good nobody will play with me, not really, I just don't have any friends)
Hybrids, a little more power than in the game, can't really use more than 1500 or so but it's fast.
Now get this, the GS code that gives the AI better hp,traction,downforce and one more I forget. So its so competitive on the same track, you can have damage on in gt2 if you llike to make it harder still.
There's a code for opening all tracks to race on, street cars on dirt, its a whole incredible world you non gs'ers are missing.