well..lets say you had 6 plants thats yielded 500g total dry weight with the 2 x 600w thats 500g/1200w a little under a 1/2 gram per watt. now lets take that same grow with 6 plants and put them on a light mover and lets also say that you yielded 400g dry weight.
400g/600w is the ratio. obviously if your using a light mover your using watts more efficiently. Does this mean ur gonna yield more per watt if your doing it right?...i have never done light movers before but i would think the ratio is considerably better then a stationary light. again this is all assuming everything else is optimal for growing conditions.