TT Gold London using GT-R in <57 sec is not that hard.
10 lap Suzuka, using JGTC, is not that hard also.
3 lap Nurb, I use Ferrari Enzo, all default, max speed 350, not that hard too. Leading #1 by end of 2nd lap.
10 lap Spa, not hard also, using Chaparal 2J with 684pp. Lead by 6/7 laps. I think using other cars can win also, if manage tyres properly.
(the above 3 races, all with variable weather and tyre wear)
TT with C7 in Nurb ring

the car slides so easily. Even my
roti canai on plate also doesn't slide that easily...
But trying to catch up with the leaders is insane.