OK ...mostly for me I quilt from the top and work my way down doing my borders as I go, working my way down as well. I have never done a pantograph but I have helped other people do them.
I have taken classes from professional quilters.
Each professional did borders differently..so I suspect you will get the same differing opinions here.
I think there is a few things you have to consider:
1. How is the piecing? If the piecing is iffy...I wouldn't even consider turning that quilt..what a headache and pucker city!
2. How heavy is the quilting? In this case you aren't doing heavy quilting probably because you are doing a panto...however if you did heavy quilting in the center of your quilt and you are trying to put a panto in the border...problems. Heavy quilting sucks up fabric...you will have to learn how to stabilize a quilt as you are quilting to get that light border design on...if you even can get it to go on evenly. Just as another responder said..wavy.
Sally Terry.....she said she takes quilts off and re-pins (turns ) then to do borders...she is the author of "hooked on Feathers"
Deloa Jones....quilts her borders as she goes.
But she is also a gadget quilter..she will use pantos, many types of rulers and stencils.
I hope that helps.....Good luck!