Actually, I've found the understeer of the ZZII can be largely reduced just by turning off ASM and TCS, or leaving TCS at a very low level (1 or 2, it does have a tendency to spin the wheels in first gear with it turned completely off). It allows you to give the car a little drift, to get through the corners at a tighter angle. It's not so much reducing the understeer as far as countering it with oversteer, but it works.
I actually became aware of the ZZII's capabilities only yesterday, if you believe it.. hehe. I saw it mentioned a couple times on another forum, and went to go test it out. Turns out I had won one way back when and never even glanced at it twice.. it was just collecting dust in my garage. But man, that thing is a monster. I daresay it's beyond a mere sports car, I'd call it a supercar. Incredibly fast and nimble.. lots of power in a lightweight, wide, low body. Ten second quarter mile and a top speed over 200+mph, right out of the box, and it can go head-to-head with some of the LeMans cars. Ain't no Skyline can do that.
Further adjustments can probably deal with that understeer, though.. All I did was shut off the driving aids, that worked rather well all by itself. I'm sure tweaking the stabilizers, suspension, downforce, etc, will do even more.