Upgrading the rear swaybar is not going to push the car into the "neutral" category.
Depending on what you are looking for and how spirited your driving habits are, get the largest front and rear swaybars you can find. Yes, even the front. People will tell you that it's only going increase understeer, but that is not the case, there is more to it than that. The gains from running the large swaybars negate the harshness added (minimal).
Even with the largest bars you can find, the car will still understeer. The active rear toe has to go. I have yet to do this, so I can't give any first hand experience impressions, but the system was designed to induce understeer.
On top of all that, replace as many bushings as you can. I've done the front with Prothanes and the Whiteline caster bushings and have a box full of bushings for the rear waiting for install.
Even at 440whp, a cranked steering wheel, LSD 4 bolt, aggressive alignment, and above mods, the car still understeers when pushed in corners. I have to get crafty with the steering wheel to get it to slide like most of want it to.