i have personally seen an led that uses 1-100 watt led with a 6000k spectrum that draws 102 watts from the wall @ .87 amps. It has a heat sink and remote driver that you describe. Its really pretty neat. Im curious as as to why they are messing around wtih the smaller wattage leds when the manufacturers are making 100 leds. The fixture i saw was running around 120 degrees- and had a nice large finned heat sink. It disspates most of the heat surprisingly without the use of fans.
The efficiency of the the leds drop with increasing wattage. IE a 3w LED is not as good as 3 1W LEDs.