hey, that is some major stretching. do you plan on low stress training your plants? check mine out. it's about as far along as your plants are. i moved the light a little closer to prevent too much stretching.
Sativas and low amounts of light will get you out of hand fast.You should just go buy a 4 foot shop florescent light to veg these in.Light can touch the tops and stops all stretching quick
Root sytem probably about ready to outgrow the cups. Transplant and add 20% perlite, as you indicated earlier. Make the new soil line about halfway up the stalks to combat the stretching.