I once set up for top speed with taller gears and lower downforce good for 370 kmh but B spec driver did not go faster than 320 - 330 kmh (long back straight Le Sarthe )even with 7000 B spec points.
He lost out on the twisty bits and did not use the top speed to his advantage on the straight. I leave settings default now and B spec seems better suited to the default settings.
Not sure on the ASM/TCS settings making a difference.
Can't remember which track I tested this out on, but with various ASM, TCS settings the b-spec driver seemed to drive the same. So maybe they are set to the default when you switch to b-spec Bob.
most car mods affect the b-spec driver. he drives worse if you use a better gear ratio. he lost on paris with the gt3 tranny trick, but whupped ass with the slower standard gearing