In regards to energy consumption, given lamps of equal value I will say yes.
In regards to plant photosynthesis, you may be over simplifying this. You can't overclock a plant. The plant will utilize as much light as there is co2 and nutrients available, anything more is wasted light energy. Depending on your setup two lamps may maximize your growth productivity.
There was an old quote from this site. Only Bad things happen quickly in an aquarium. Good things take a long time to happen. I believe HOP is the author.
Have an open mind, but not so open that your brains fall out.