it's wonderful that you've tried all cars. but something from my experience i'd like to share with you, i've tried all cars also. For drag, my suggestion is Pandiac GTO, great engine, no much turbe lag. i can do it under 7" & 10". For drift, RX-8 is nice, agree with you.
Grip, the most wonderful car is Pagani Zonda F, I run it in the same track faster than Mitsubishi EVO about 5", and faster than 911turbo about 4" and Ford GT about 7". Speed i am using Lamboghini.
Actually, not all cars turned to the max (level 4) will be the strongest & fastest, there are the balance, not all cars' suspension & brake can fully suffer the imgines, i.e. EVO IX, imgine is great, brake is rubbish. Moreover, my 800hp 911turbo is much faster than my 1000hp GTR proto.