Need Help With my Next Tire Setup..

Endgame

O.K. I am trying to figure out what to expect with potential tire setups so that I can decide on which tire sizes I will go with next. The problem is that I have NO idea about tire setups and their effect on handling on our Z's. My goals are:

1. To have an aggressive street driven car that will see some autocross and track duty (just for fun).
2. Increase turn in/reduce understeer (or at least not increase it)
3. Maintain straight line acceleration

At the time I purchase my new tires, my setup will be as follows:

Stance Coilovers (these may change to APEXi)
Stillen Sway bars (probably set to the softest setting)
Wheels: F: 19x9.5 R: 19x10.5
Tires: Nitto Invo F: 245/40ZR19 R: 275/35ZR19

I am considering changing my tires to:

1. Bridgestone Potenza RE11's F: 245/40R19 R: 285/35R19
2. Bridgestone Potenza RE11's F: 255/35R19 R: 285/35R19

Which would be the best set up to achieve my goals? What type of results can I expect?

Thanks for the guidance all!