If you have exhausted all other attempts to shift more grip to the front vs. the back- like adding more castor in front and playing with both front and rear toe settings, then you might want to try that new stiffer rear bar.
Very tight corner turning ability is most affected by front castor and rear vs. front roll stiffness ratio. Either approach unloads the inside rear tire. The advantage of using more positive castor is that it only does it with more steering lock. If you do use castor, be careful to not get behind in slaloms and turn the steering wheel too much, or you will be prone to spinning the car.