I love your quilt and recognize all the effort that went into it. I have a border idea that I have used that came from a wall hanging of a salamander pattern that was done in primary colors. I call it "zip strip". You use all your rainbor colors as you go around the quilt and cut the ends where you join them on the bias. That seems to give movement to this. Put balck borders on each side to get the size you want. Since you used strips already cut, no extra labor involved. Bind in black to not destroy the effect of the rainbow strip. Hope I have explained this well enought, but if not, PM me and I will post a picture of the salamander.