I haven't visited this forum in a long time so I don't know if this has already been mentioned. I just installed the $20 Coleman Max Ultra High Power flashlight (3 AAAs) on my bike.
I previously had the 110-lumen version mounted on one side and the Cateye EL530 on the other side, plus a headlamp. I tried out the 150-lumen version last night and found it to be much more powerful than the 110. The specs says the throw is 400 feet, but I was able to illuminate reflective signs at least 600 feet away. The spill was excellent---it covered the entire road, with a large bright center right about where I wanted the most illumination. I forgot my headlamp but didn't need that or the Cateye at all. The Cateye didn't add any appreciable light to the Coleman 150.
I'm pretty amazed: a single $20 flashlight is sufficient for safe riding at about 12mph on a country road. I'll still use a headlamp to light things along the side of the road (like animals), but I'm not going to continue using the Cateye.
I don't think two of these flashlights are necessary but if you had two that would give you a heck of a lot of light.
Run time is 3 hours so I will get rechargeables to avoid adding batteries to the landfill.