the human eye is does not sense light in a linear fashion... i.e. a doubling of light intensity doesn't appear twice as bright. In fact, a doubling of light is noticeable, but looks to me more like a 30% increase.

Most of my bike commute was on dark rural roads. My light was LED, with LEDs that produced about 100 lumens per watt. With 3 watts from the dynamo, that is about 300 lumens. This was plenty for me. Beam pattern makes a big difference, of course, but my point is that with a decent beam pattern, 800 lumens sounds like it would do the job for you.

Now... who wants to discuss beam pattern?
There must be a number of threads in the past.

Steve in Peoria