For me it has to be winning at Suzuka with my Integra. That damn course gave me so many headaches. I cursed it many times and cursed the Japanese for building it. I finally won though and it was sweet.
Nothing will be as good as the 750pp HSR race I, Mines_GTR and 2 other GTPs had. We raced the last 3 laps 2 wide and 2 wide. Last lap went 3 wide on turn 1 and 2 followed by 4 wide on the bridge and back to 3 for the S turns. 2 wide through the tunnel and 3 wide on the last turn. I finished 3rd though after hitting the wall on the last turn.
I really think the Japanese cars do best on the Japanese circuits.
My greatest win was probably on A-8 with the F430, was so close to winning every time, then I finally did it. Catching the lead F430 happens to be one thing, passing it is certainly another. Took me 4 hours