Well, I just put a level 2 Bob in the Ford GT Spec II Test Car for the American Championship Indy race, and he won with very little encouragement. Not sure that means he's better, though, because I think to win it the first time I put a new Bob in the ZR1 RM because new ones brake later (part of being a worse driver, apparently), so I'm not sure. The problem is it'll be very hard to distinguish placebo effect from reality with this, as bad Bobs did win races before.
Although I was surprised at this Bob's tendency to actually pass people and stay alongside other cars when taking the corners, so who knows?