Well I think that's fine, about what I'd expect. I'm using a pair of 150 HPS backed up with 105W of CFLs.
You're growing in coco now? I've been using a locally produced coco base for about 18 months now with great results. The mix is almost all coco, I went through a spadeful and found - like it says on the label - tiny bits of roasted clay, silica sand, greeny pearls that I guess are the slow-release ferts "good for three months", Perlite, and couldn't spot the sphagnum moss or lime that's supposed to be in it.
I found with this Aurora that even with the presence of the ferts in the coco, the mature plants could take 3x the recommended concentration of Miracle Grow 15-30-15 in the water. What a glutton for nutes this strain is!
Northern Lights is one of the parents of Aurora, isn't it?