A level 35 Bob should be very, very good.
He should be able to win in cars somewhat better than the competition, rather than insanely superior.
However, there are a few things to bear in mind. I always run endurance races with a single driver who never gets a break (obviously). In that case, he has to drive the whole race on cool (not that you're going to be there to change that all the time), and he's not going to corner well.
So you need a car that handles well, and is much better than the competition.
But I've won endurance races with very low level drivers. It's not all about the bob's level. Some Bobs are great with certain cars, and not great with others. If you have level 35, you've raced him in a fast car many times. I suggest you go with the car he's won a lot of races in in the past.