slvoid

Well I have the cateye el 500 and light and motion dual and I've compared the dual against a 13 watt HID.
So from there, they're just my experiences that I've tried to put onto the table.
Anyway, in case someone's wondering, here's how I got the speeds for use in the inner city.

=ROUND(IF(LIGHTTYPE="Halogen",(-0.0002*WATTAGE^4 + 0.0143*WATTAGE^3 - 0.4048*WATTAGE^2 + 5.5274*WATTAGE - 9.2313)-2,IF(LIGHTTYPE="HID",(-0.0002*WATTAGE^4 + 0.0143*WATTAGE^3 - 0.4048*WATTAGE^2 + 5.5274*WATTAGE - 9.2313)*1.75,(-0.0002*((WATTAGE+4)*1.1)^4+0.0143*((WATTAGE+4)*1.1)^3-0.4048*((WATTAGE+4)*1.1)^2+5.5274*((WATTAGE+4)*1.1)-9.2313))),1)

Then I take that and stick it into the formula below to get max speed usable on a clean road outside the city.
=ROUND((0.0000001*CITYSPEED^5 + 0.000004*CITYSPEED^4 - 0.0009*CITYSPEED^3 + 0.0224*CITYSPEED^2 + 0.0854*CITYSPEED + 0.8849)+CITYSPEED,1)

And the average is =ROUND(CITYSPEED/1.5+ROADSPEED-CITYSPEED,1)

Then during my break at work, I just compiled a list of lights, bulb type, battery life, and wattage.

The 4th and 5th order functions are based on polynomial curve fits of what I felt best worked for me both in the city and outside the city on a dark relatively clean road at certain speeds.