I think I made the point in an earlier thread about the F1's making the game too easy that the beauty of the whole GT series is that you can make it as easy or as hard as you like, like seeing how far you can take a race-spec Lancer coupe in GT1.
I tried this too, I used the GT-one, and beat the first 3 races. Whatever the forth was, I just couldnt keep up with the last place and got discouraged. It gets harder, so good luck