[TrqlessWonder]

Well, to answer the original question, I did my first event in the rain on stock everything save for an initial alignment, and ran at 37F/34R Car was lively to be sure, and I did spin it once, but I experienced no understeer with it. Just had to be a little patient/smooth on corner exit.

As for the erratic/unpredictable behavior, it's hard to tell how much of that is car versus you. However, looking at the specs for your springs, I think they are part of your problem. Especially if you're still on the factory dampers. For autocross, those springs drop the car too far. The fast guys are only dropping 20mmF/15mmR. Check to see how much you're hitting the bumpstops. Whacking bump stops will make most any car a handful, and kind of invalidates any tire pressure recommendations, or thoughts about spring rate suitability.