You can grow SPS with them, but they're not as powerful as you might think. Vivid Aquariums is doing a side-by-side comparison over an 800G aquarium using 12 Radion LED fixtures (1680W total) and 2,800W of Radium MH (2 x 100W and 2 x 400W). The PAR values for the Radions are significantly lower than the MH.
The details of the experiment are here:
http://www.vividaquariums.com/aquariumLightExperiment.asp
There's a Youtube video of the tank here:
http://www.youtube.com/watch?v=IpJM...ryvsUo3hcngtLQ8&lch=email_reply&feature=email
It's not necessarily a fair comparison unless they match the PAR between the MH and LEDs though. Another mismatch is between the spectral characteristics of each. They should be configuring the LEDs to match the MH spectrum as much as possible, which they can do with the Radion configuration software.