The tires will go a long way in communicating road conditions, traction limits, etc... (I assume you mean 205mm ) Many autocrossers get pretty oversteer-biased suspension... but you really don't need it to do well in autocross. I find my 400f,400r spring rates to be a tad on the understeer side on the street, and pretty neutral (although pretty easy to provoke into oversteer) once I've dialed in the shocks. But there's no need to follow the herd. You don't need an "autocross suspension"--whatever that is-- to autocross.

If youre just trying to get a handle on your car's attitude and behavior at the limit, really the last thing you should do is start modifying the suspension. Find yourself a big, empty parking lot and have at it. Only once youve mastered the stock suspension will you know what you want out of a modified suspension.