I think there was a formula somewhere on the forum about the efficiency of toroids..maybe in the range of 90% +.
Ecores, maybe they are 80%..not sure but I know I never had luck with ecores..besides being bigger in size and easier to wind. I have a few I got out of the flourescent light bulbs that Brett posted a link for..Or was it Rob.. whoever it was...anyway, they are alot smaller and you'd have to use really fine wire for the secondary or getting the 400-450 turns would be a real chore. Actually I use a 1/8 inch x 1 foot length of hardwood dowel notched in a v on both ends for a shuttle for the toroids..makes it a breeze to wind em.. 20 minutes tops and I have 450 on one.
Tonight I have finished 2 of them while watching TV.. Ready to wind the primaries..

I'll have to look up that rating for the toroids.. we can compare notes and see what is better to use.. Beginners would have a tough time with em.. so maybe E-cores are best for most..

John