I like the Cizeta, too. It actually handles pretty nicely - at any rate, it's interesting to drive - and its stopping distance is fairly realistic, unlike almost all GT4 cars. It's also one of the best sounding cars in the game, IMO.
Seismica, I read your post and couldn't resist. I took the car bone-stock, including leaving on the stock Sports Medium tires, to the Dream Car Championship race at Test Course, and fairly easily beat a field that included both Ford GT LMs (two of the fastest cars in the AI "pool") for 200 points. I then added a supercharger (804 HP, if I recall correctly) and a fully customizable transmission and entered Like the Wind, beating a Toyota GT-ONE after appropriately timing a pass in the last corner. I'm confident that with some finagling of the lineup to include only the slower cars in the Dream Car race (no Fords or Zondas) and only slow cars or cars that pit in Like the Wind, both races can be won with the same basic modifications that I used in addition to N2 tires (or even N1s), which provide what I believe to be realistic grip for this car.
And yes, I know what you meant. This car has no chance whatsoever in a "normal" race for 200 points because it isn't blessed with enormous amounts of grip. On second thought, though, it's conceivable that it might be able to win the Dream Car race at La Sarthe II against the right lineup (one that allows the use of relatively soft racing tires). I'll investigate that now.
Edit: I just won that Dream Car race for 200 points against a field including both Ford GTs, the GT-R, the RX-8, and the XJ220. I used NA1, R2 tires, racing brakes, and a fully customizable transmission, and it was nearly a completely clean race. I always kept two tires on the track (counting the dusty tarmac areas as off-limits), and I made no AI contact, save for when the GT LM Spec II ran into me in the first Porsche Curve on lap 1 on his way past. There's no question that it could be won more cleanly against a somewhat better lineup; this one had the GT LM Spec II starting in first place, and the Mazda and the Jaguar drag down the points. The ability to use R3 tires would definitely simplify the race, even if a little bit of ballast turned out to be necessary.