LED's for a 4x8 tent? need info

I'm gonna try growing with LED's soon but what should i get for a 4x8 tent in terms of wattage/actual wattage and spectrum?
Currently using 400w HID's + 200w cfl's for sidelighting

And do LED's really cut the electric bill cost?
How's the yield compared to HID's?

Enlighten me please.

LED technology is always evolving. Many of the commercially available LED fixtures use high wattage elements, which radiate heat as well as light. If it uses a heat sink, then it's losing energy to heat, which you're going to see in your electric bill.

They are still generally more efficient, and there's no bulbs to buy. Most LED's operate for hundreds of thousands of hours. I don't know how they perform with plants, but the ones that only use red and blue spectrum light must be more efficient since they're not wasting energy producing light at frequencies that the plants don't use.

I'm currently building a grow box for mothers and cuttings that will use warm white elements. Haven't seen any that are really impressive as far as efficiency, and haven't heard anyone raving about them being better at growing good healthy plants.