Your quilt is beautiful!!!!
I have the Grace Frame that you mentioned. I bought it thinking that it would be easier to use than a hoop on a large quilt I am planning to make. (about the same size as yours) First of all, this frame is BIG! For your quilt you would need about 10' of floor space to set up in, and expect to leave it up the entire time you are quilting. My original plan was to set it up in my living room, but that idea was squashed when I realized the time and space involved. So....I devoted an entire room just for the frame, and began with a crib sized quilt just to see how it went.
The frame assembly is a BEAR! You will need to be pretty good with tools and following directions precisely. I spent about 12 hours on the assembly, and needed my husband's help on the final part, since it was just too large for one person to handle. I assembled it in the King size, then had to disassemble, and reassemble into the crib size when I changed my mind on the quilt I was making. Geesh! There went another several hours!!
There are You-Tube videos explaining the process of putting the layers onto the frame....top...bunting....and backing. Again, follow these instructions precisely! I think this must be where I screwed up, as my top does not perfectly align flat onto the other 2 layers.
I am almost finished hand stitching this little quilt, and it is precious, but I do not think it is the best plan for a quilt this size...the hoop would have probably been easier. However! I do plan to use the frame for the king quilt I am assembling. Like you, I am worried about the fabric shifting, the heavy weight of the quilt on my as I sew (maybe this should be a winter project!!) , and the hoops stretching my fabric. At this point I am undecided. And frustrated to say the least. I had hoped the Grace Frame was going to be the answer, and maybe I need more time and experience on the frame to get used to it, in all fairness.
I know this does not answer your question, but it may give you some insight to what you are up against if you buy a Grace Frame. Below is a photo of the frame assembled for a king size quilt.
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