I drove my Yellow Bird a bit more last night and was not able to make any improvements whatsoever. I hate this point in tuning in GT6, where each change you have made so far has made noticeable differences, but the tune has now plateaued. In slots A, B and C in the tuning menu, I currently have loaded three very different suspension settings. I have transmission, LSD and ballast where I want them, so kept them consistent across the tunes.
Tune A - super soft springs, hard sway bars
Tune B - hard springs, soft sway bars
Tune C - a hybrid, kinda down the middle
All three tunes are nearly the exact lap time, down to one tenth, which is frustrating. One is super easy to drive, not afraid of the curbs or bumps and easy to save if overdone. One carries tremendous corner speed but touch a curb or a bump or miss an apex by the slightest amount and you are heading toward an off-track experience. The third is really the dogs breakfast and not at all performing like a hybrid of the two.