Clones have problem with 400W MH

[stinkyattic]

1) Is it worthwhile to leave these plants for a week outside and then try again? Of is it possible they received too much stress and they will remain problematic?

Go ahead and keep them. They just need time to adjust to strong light.

2) How do you determine if a plant is ready to go under 400W MH?

It should have excellent root development. You can keep them under CFLs much earlier.

3) What is/are the reason(s) a plants starts to hang under 400W? I read that it is possible that the roots have not developed enough, any other possibilities?

Yup, you don't have enough root mass to keep up with the increased transpiration rate triggered by very bright light and heat.