Some LED headlights do continue to get brighter at higher speeds, at least up to 20 mph or so. At higher speeds the extra heat generated may limit brightness, except on lights designed for high speeds like the Supernova E3 Triple. Here's a chart for the Edelux, which compares the brightness at each speed for that light, versus their halogen bulb (E6) (yellow line), and I believe the Lumotec LED light (gray line), and a competing 1 or 2 watt LED headlight (blue line):

http://www.starbike.com/images/SON/e...ngsstaerke.png



The brightness reaches 15 lux (as bright as a halogen light or an older LED) at only 3 mph / 5 kph, and levels off near max brightness by 12 mph / 20 kph. But the brightness increases a little bit more up to 18 mph / 30 kph, at least. I doubt you would see a difference.

Anyway, back to your question about hill-climbing, as long as you can keep the bike moving as fast as a brisk walking pace (3 mph), there should be enough light to see the road in front of you, but the light will not be as visible to oncoming traffic (as usual).

I think the B&M IQ Cyo and the Supernova E3 Pro would have similar lines and similar brightness.