F1 2014 Choosing Difficulty in Career

[Hatch]

I asked a similar question last year but still haven't quite got this down.

I normally play on Professional difficulty in 100% career mode. But I seem to have a large time difference in relation to the AI on different tracks. i.e. Albert Park I seem to run about a second faster than my teammate and then at say, Spain, he's 1.5 seconds ahead of me.

How do you guys pick the best difficulty for each track? If I try to use practice times, I either run away from the AI or get smoked. There seems to be no in between. I'd love to run a tough, challenging, head-to-head battle with my teammate but can't seem to dial it in.

Thanks for any advice.