I tried out the "GT6 Suspension Wizard" thingy and I got these results.
BMW M3 CSL - Turned it into a 550PP monster, can potentially chew up, gargle, and spit out Elises.
Lamborghini Aventador - I was about to give up on this understeering nightmare, but I found a way. Now, I'm doing 1.58:xxx on Silverstone with it. Pretty sweet.
Ford GT - Track tuned, it carves corners like a Christmas ham.
Mazda RX-8 - Bought it, fully tuned it, fiddled with the suspension. Now oversteers like a mother.
Alfa Romeo 8C - I was pretty impressed with this when I fully tuned it. It got around 2.00:xxx around Silverstone.
SRT Viper (2014) - I attempted to tune this for track instead of the typical drag purpose. With the exception of a wee bit oversteer when you punch the throttle, this is the fastest track tuned street car I have right now.