I think the more you ride, the quicker you get at defeating the hills too. I changed my commute a couple weeks ago, it's a little longer, couple of miles, and all rolling hills. But, it's not full of crazy drivers. It kicked my butt a little at first, but already the hills have started to flatten out, and I'm only a dozen or so commutes in. So overall leg stregnth and conditioning effect the curve as much as terrain does.

Love those rolling hills, they are good for sprints.