I started this summer's crop with 10 cfls at 2700K and started to flower at about 6 inches now they are about 2 feet tall even with the Lst. Strectchin like a bitch.
Not only light spectrum affects stretching. Night/day temp difference, watering, and specially, light intensity.

The most common error when growing with fluos or CFL are dont give enough importance to reflectors, wich are esential. And using too small watage bulbs and tubes, wich are less efficients and give less intensity.

Good luck in your grow

knna