Depends on your suspension height really but with a little arch rolling quite a few people run 235/40 on the rear.
I,ve just about got 235/40 kumho v70 to fit on the front as well with a little persuasion not tried these on track yet though.

TBH for the last few yrs my favourite for track has been 225/45 16 all round. Was running these last Sunday at National Day.