I starting playing with my selection of border fabrics today trying to find one that might suit the Wrench quilt. I already discarded two - one because it colours were too "cool" and the other too "warm". the first one was purple/pink/blue and the second mustard and black. Love them both, but not with this quilt.
I love the chocolate with turquoise. Brown goes with everything and the blue brings out the splashes of blue in the quilt. Also, if I use this one, with the brown closest to the blocks, then I don't have to do a narrow setting border as well.
When I put my border on I do not try and mitre the stripes in the corners. I know this is a popular technique, but I found that it was a technique devised some time in the 1970's and not really a traditonal feature in the mid-1800's, which is what I try to make my quilts look like. It also wastes a lot of fabric, and I am too stingy! I put the side borders on first, then the top and bottom.
The borders should be cut from the length of the fabric where possible, as the long threads (the warp) are far more stable, and the quilt will have a much straighter edge. I know that sometimes that is not possible. You just have a small amount of fabric, and it is just "the perfect" one, so you want to use it, and cut across the fabric and join it. I do that too, but when I can I use the length.