So I've been autocrossing with the stock 25mm front swaybar for 5 years. Over the years I have seen several pictures of my car and felt the rear-inside wheel lifting & slipping during sweepers. According to Fred Puhn, this is a classic symptom of an insufficient front "anti-roll" bar. So I dialed up a heavier sway bar in GT6, and in the simulator the Crossfire felt better in turns. So I ordered a Front 30mm H&R from ECS Tuning for about $250. According to Fred's calculations going from 25 to 30mm is just under 100% stiffer. So I installed it and took it out to the track for an autocross event that had 3 Epic Sweepers (I was in third gear for two of them) and the H&R really flattened the car out in the turns. In addition to the sway bar upgrade, I did lower the rear about 1/2" and was running new 245 A7s up front and 295 A6s in the rear, so there was some additional improvements, but the H&R was a big help. I didn't seem to generate any more understeer, but that may be simply offset by the new tires. One of the faster Z06's used to be faster than me by 3-4 seconds in a 60 sec event, and he was only about 1.5 sec faster yesterday (fortunately he is 3 classes ahead of me). I will monitor it throughout the race season. For the money, I would recommend it to anyone wanting to autocross competitively.
Mike