Is a real race driver a good sim racer?

I have been wondering this lately, wanted to get some opinions. I have seen a few people use my rig that have high performance driving experience, but no sim racing experience. Both of them were pretty good for first timers, but they would still have to practice a lot to get good. Sim racing is supposed to simulate real cars, but these guys had difficulty judging corners and speed just like everyone else. That said, they were improving quickly.
On the other hand, I know the reflexes on the wheel and pedal are honed in both sim racing and real life so the skills transfer.
Sim racing is in some ways more difficult because of the limited feedback, of course we dont deal with the fear of injury or death. Many real drivers sim race and vice versa...but for the ones that dont I speculate how competitive they would be. As technology improves this may change of course.