No car is strictly "off limits" except the X-bow, the only rule regarding car choices is, aside from the no concept, race, rally and tuner cars, that should you win you cannot use the same car for the following race.
I try to post my lap time and sometimes so do some of the others here.
Currently I've managed 2:08-2:11, so I would expect the times for the best drivers here to be around 2:04, maybe even as low as 2:00.
I always try to use my S2000 to give a baseline for everyone to compare to.
Hypothetically, if you do use one of the "cheat" cars and are much faster than the times others are getting, you could be in for quite a lonely race.
The onus is on you to use your best judgement about your need to use driver aids or a "cheat" car.
This is supposed to be casual and fun at the end of the day. You can make your own challenges for yourself. For example running no ABS, or turning off SRF if your an absolute beginner.