Gorgeous quilt. I really like the flutterbys for the body. Maybe the spiral border because it has a softer look to it than the popcorn. I have used a butterfly pattern from Pat Cody's book, Continuous Line Quilting Designs called flutterbys for borders. It's a simple pattern and I do free motion on my standard Bernina. I've never used a long arm. Is there any way to modify the flutterby body pattern into a border pattern?
Good luck, but the quilt is so beautiful and the pattern so busy I would keep the quilting simple and open.
Just MHO.