well the XM-L has a higher intensity then the XP-G R5 and also use up slightly less voltage so you can put more on one driver.
as far as i'm concerned at this poiunt with the depths of our tanks it is still not needed, but if you do decide to get them you could always run them at lower power which will help save the life of the LED
, its really your call which you would want and what you think is worth while to do.
greg there is also the fact that those LEDs are pumping out more wattage then the more powerful LEDs, no one doubts that they grow and work well, but is the longevity of the LED
the same and the power consumption. to light a 180 you need 3 of your 240watt fixtures totalling 720watts where you can go with 108 cree LEDs and put out 324 watts and still put out the same if not more PAR