I'm not crazy about variegated thread. When the thread color matches the fabric color, the thread disappears; but when the thread color contrasts with the fabric color, the thread jumps out. That can actually add busyness.
For a busy quilt like this, I would probably choose a fine neutral thread. Jamie Wallen claims the Isacord "baby poop" color (#0232) disappears into almost any quilt. If not that one, I would probably go with a Bottom Line thread in silver (#623), which Bob Purcell of Superior Threads claims disappears into any fabric.
Here is a link to Jamie Wallen's site:
http://quiltersapothecary.com/thread/isacord.html
And here's a link to Bob Purcell and the Bottom Line silver he recommends:
http://www.superiorthreads.com/video...ine-polyester/
http://www.superiorthreads.com/shop/...yester-thread/
Also, I would suggest reconsidering doing an all-over crosshatch (crosshatch in the borders would be nice). This is already a very geometric quilt. Straight lines of quilting are always going to deviate somewhat from the straight lines in the quilt, even if you use the ditches as a guide. Plus, curving lines in a geometric quilt add softness. If you go with an all-over meander or any kind of curving quilt design, it would add some softness and contrast to the geometric pattern of the quilt. I do think that straight lines (keyboard) or crosshatching in the borders would be very nice, as they would enhance the geometrics of the center portion of the quilt.
Edit: One of my favorite quilting patterns for this quilt would be Baptist Fan, but it is relatively difficult to do with machine quilting.