I'll assume thats as much negitive as you can pull from front and rear...
Id keep the fronts where they are and probably drop the rears to 1 degree or a bit less.
That should at least keep it balanced as far as grip...and then you can use tire pressures to tune from there.
I'd stick with your current setup for awhile, and really concentrate on learning the car. Get to the point where youre really consistent, and then upgrade. I recently went to wider, but lighter wheels and tires, and im still trying to "relearn" the car.