I'm finding that very hilly courses aren't as amenable to my HR based workouts - the steep parts are fine as I just go slower, but the downhills are often too steep and curvey to maintain the target HR (or power for all you powermeter guys).

I'm finding that the flats are a better place to pace - you can go plenty hard on them as well.

Anybody finding this?

(Of note, I have no difficulty climbing steep hills - I routinely do one around here that's 21% for quite a ways.)