We've got a bunch of guys tracking and auto-crossing their cars on our RCE Yellows regularly...lots of happy drivers.
One thing to keep in mind is that the front and rear have very different suspension designs, so in increase of X% at the front doesn't necessarily = an increase of X% at the rear. The front is a strut and a little extra rate goes a long way towards keeping the car geometrically happy. Better turn-in as well while keeping the rear controlled makes for a fast and confidence inspiring car. Understeer is not an issue.
Stock and a lot of the softer rate lowering springs that drop an inch or more are very bumpstop active in cornering, so the spring rate gets a little spikey in heavy cornering. Makes it's easier to overload the tires, leading to understeer. With our firmer front springs, mild drop, and shortened bumpstops, things are a bit more linear and consistent.
As for KW V3 vs. Koni + RCE Yellows....as a vendor for both set-ups (except the Konis, get those from Strano or TIC) it really depends on your needs. The Koni + RCE set-up is simple, fun, fast, and cheap. It's kind of the easy button, put them on get a good alignment, and go have fun. If you're a bit more serious, running fairly sticky tires, like fiddling with adjustments, or you are looking for a little more of an edge for auto-x or the track, than the KW V3s will do well for you. Or RCE T2 Clubsports (based on KW clubsports).
- Andy