Light vs watt... I would say below spec driven LEDs would be more efficent.
Latest news I can find about cree (one of the most efficent brands)
CREE |Cree 231 Lumen Per Watt LED Shatters LED Efficacy Records
And a good read about Led efficentcy vs watt usagage etc.
White LED lumen testing
Seems the newer Cree leds should be at or above 100lm\w at say 350ma-400ma draw.
Side note on this, there is a graph in that thread (somewhere around the 9th page) which shows date vs led efficencies with a good up trend for best, and worst being almost flat lined.
I tried to do a quick search on HID LM output vs W usage I found a like on this site! Another great read. All in all, I think correctly designed LED application should be the best bang for power usage and $ with some fab skills.
EcoFit Lighting
Oh and one more thing to remember with "raw" LEDs, you must limit current in some way. Resisters are simple but lowest efficency while a dc to dc constant current driver is probably the best you get (80-90% max). I do not know if HID lights are measured with or with our their power drivers, more research is needed >,<.