They're hard, but you get a lot of ego for them.
I almost think that the bonus' you get by leveling up your runners helps you in the challenges. So you might want to wait until you level up (or max) your runners before trying them. I finished this pursuit before they nerfed it with my runners around level 5... (with the exception of the san francisco area ones since you couldn't get there before a portion of storyline at that point) It's not really skill, it's more persistance and always drive to the end, even if you don't make it... it'll help you get used to the end of the track as well as the beginning... Just note slow-downs or things you hit, and try better the next time, and the next time, and so on... There were a couple that it took me 10+ tries on, but I made it eventually... Keep your calm, and you'll do better.
Edit: I also did them on this newer account after the nerfs and such, and it was a little easier, but still not as easy as it could be... it's still a lot of EGO to miss out on, just hang in there and keep trying every once in a while.