Big V with any handling problem you must determine under what condition. Does the understeer occur at entrance,apex or exit? Also the high speed oversteer , what condition?
As for the big negative camber , that works great for turning but under braking the car will very likely be weaving around on the inner two inches of the tires making the car darty on the brakes. I bring this up because it is a familiar set-up problem....the car is a tiny bit darty on the brakes so instead of trail braking into the apex the driver gets back on the gas to settle the car , which in turn unloads the front end and presto you get understeer.
If your car has to much toe in you will likely have to trail the brakes all the way to the apex anything less will result in undesteer.
Toe out will of course make it darty on the brakes and likely result in high speed over steer. Mismatched sway bars front to rear will cause this as well. If the rebound on the rear dampers is a couple of clicks to stiff the car will likey oversteer in fast kinks and undsteer in medium sweepers. The car will jack down over bumps unloading the front end , progressively building understeer.
Driver factors in here as well; I steer a car with the pedals , read trailbraking and throttle steer. Most experianced drivers rave about the handling but one friend who has driven it , thought it understeers a bit. He isn't the smoothest driver and tries to pinch the wheel while on the gas....simply won't work.
sorry to be so verbose but without knowing the conditions and your driving style it is hard to say; My guees at this point would be check the toe and soften the car up a touch so it is not skating around so much. Also if the tire temps permit I wouldn't run more than 2 dergree negative camber.

Tom