I used to shoot a lot of existing light photos back in the day when we used silver instead of silicon, but the same principles apply. I found an ISO of about 800 seemed to come closest to what I saw with my eyes. To this day, I still use ISO 800 when I shoot existing light.
Agreed, 800 is a reasonable speed for existing-light shooting. Here's the Philips Saferide at 800, haven't taken photos of the Luxos yet.
Philips SafeRide Bicycle Headlight Beam Pattern by
joshua_putnam, on Flickr
And here's a different view of the Saferide,
Headlight Beam Pattern, Philips Saferide by
joshua_putnam, on Flickr