alright more info, so i built 3 variants of IS and here's the deal:
Altezza (JDM): it is no good at this PI. The rear will spin out quite easily because of the wheel is only 245/245 while the engine pumping out 389 horses.
IS300: Reminds me of the RWD 03 fairlady Z, great promise but a bitch to tune, wheel constantly spins out, thought not as limited as the Altezza, it's versatility is not as good as the IS350.
IS350: Very versatile because of the very wide rear wheel. Can be either built to good power for long tracks or an acceptable car on short tracks. I wouldn't mind using this in the race.
Cons for all 3: Slight understeer. Not a grip car, we might have a problem on Tsukuba due to how easy it is to spin the rear. Also they seems to be very jumpy for some reason, not that they take off, but you can feel it jumping up and down more than the other cars, i can see it's an annoyance to watch but doesn't affect driving.