Well, I was out mountain biking with them for 3 hours last night - one hour in the dark. No problems there.

On the road, I usually cuise at 20-25, and have no problem not out running my lights.

It is roughly 75% of the output of a halogen motorcycle or car (single) car headlight. Think that is enough?

It has a very useful beam pattern - both a wide flood and a tight spot. So it is good for tight turns (wide) and for high speed (far). For relatively cheap it has opened up the world of night biking to me - in places where there is no ambiant light. The build quality isn't the best, but it is a heck of a bang for the buck! It is about the size/weight of a AA mini-mag light. I just mount it on my handle bars, and I also have a light weight 50 or 100 lumen light on my helmet for tight turns. The 900lumen light just washes those out though. There is no comparison.