Yes, I did consider this. I expect that it will be 550 or 650 fill-power. Anything over that would be tremendous. But at $30 for 3oz of down... I'm saving myself nearly $100. That was a big enough savings that I considered this project worthwhile. This is one of those "use-what-you've-got" projects.
After more reading and looking around, I don't know what to do about the shock cords along the length of the sides. I think for now, I will plan on sewing in a tieout loop at each corner and if need be, I can go back and insert the shock cords along the long sides if I think it is needed. Hmmm... Thanks for the help everyone.
I always forget and make it more complicated than it needs to be...it's just walking.