123's have similar performance to the KU36. I'd be running them 36-38PSI hot.
Long term, nothing smaller than 255 should even be considered, on all four corners for the track.
Yoki do a 255 and 265 in R18, Hankook do a 255,265 and 275 in R18. Though the Hankooks are generally a 35 profile and make the tyre a lot taller.
18x10 +25F +35R with a 265 fits on my car no worries. However 18x10 +23F 18x10 +33R and a 285 is on the very edge of tyre destruction.
Grip for grip, the Yoki's are more progressive and grippy during lateral slip (around corners on the power), while the Hankook's are good on initially turn into the corner. Have to see what the 2R compound AD08R are like in comparison. Now for Yoki to stop making tyres for S2000, Evo's and 86's and make some decent sizes, like 285 and 295!!!