I have set quite a few of my clients up with LEDs, and I can tell both from experience, but more so from a scientific stand point there is a wide varience in quality and output.
For one PAR does not necessarily equal output of useful light energy.
For example (an extreme example to make a point), the green spectrum is basically useless for plants, so you could have one LED that emits only green emitters with a PAR of say 150 µMol•m²•sec while another light has exacting spikes in the key PUR areas needed by plants and only has a PAR of75 µMol•m²•sec, the SECOND LED is actually the better light as the first has basically NO PUR!
As for Kelvin, 6500K is generally best (again how the light arrives at this varies greatly). For tanks much over 24” in depth, you might consider mixing in 10k to 14k light
The LED I strongly suggest with the best warranty and highest output in PUR is the TMC AquaRay GroBeam
Please reference these articles too:
For a comparison of Warranties (this is a simple read, that makes some excellent points without having to know much about LEDs):
http://aquariumopinions.com/2013/12/16/aquarium-led-warranties-reef-or-planted/
For an overview of Aquarium LED Lights
http://aquarium-digest.com/2010/04/11/led-aquarium-lights-lighting/
GroBeam Review (the review covers the tiles, but equally applies to the strips too from my experience):
http://aquarium-digest.com/2011/12/19/tmc-grobeam-1000-customer-review/
For just darn good lighting information:
http://www.americanaquariumproducts.com/Aquarium_Lighting.html
BTW, as per the WPG “rule” this is very outdated and cannot be used to compare “apples to oranges”. In other words, you cannot use WPG to compare a T5 with a T12, or even two different LED brands.
As an example, the GroBeam LED needs only about .6 watt per gallon (that is 6/10ths of a watt), while some others require as much as 2.5 watts for the same results due to much more waster energy and poor PUR output
