I just fired up the LEDEngin 660nm array and am going to have to do some modifications.
The LED spec sheet gives a typical forward voltage drop of 3 volt at 1100ma to 1200 ma which was my design current range.
Everyone of my LEDs measured out below the minumum voltage value of 2.48 , with an average of 2.43.
This means I have to add another 2 to 3 LEDs (which I don't have room for) or use a big friggin power wasting resistor since I am running a 24 volt power supply
This also means they are going to max out at 3.8 watts per LED and realistically run them between 2.5 and 3 watts.

Using other brand LEDs, they always are close to the mid-range typical value and I have been able to base designs around this.

Anyone scratch building with these LEDs really needs an adjustable digital readout power supply with voltage and current regulation in order to check specs of each LED before assembly.