In regards to stem growth versus foliage growth, that's part of the reason I'm so sold on regular sunlight. All of my plants that are sitting under the 1000W HPS grew maybe an inch up, and then dumped their baby leaves, and started growing for real.

The plants getting sunshine however, grew maybe half an inch, and started growing their real leaves days before. I don't know how to explain it.. they just look healthier. It's a few different factors.

The only thing I'm noticing about window light that I don't like so much is that the plants are straining towards the light, so every day I have to spin them 180 degrees. I think that will be taken care of by the morning / evening HPS lighting though; any pulling to one side that the plants do because of the sunlight coming through the window will be countered by the direct overhead light from the HPS.