Cedar

So I found my perfect border fabric on clearance at fabric depot and bought all they had left (I would like to use some of it will be used on the back) It's a brown, so contrasting, but it should frame the quilt nicely and I'll do decorative stitching over the patchwork in a matching brown, so color choices are done.

My first question is about size. The quilt top is 5" squares, so 4.5" finished. I would like to add at least another foot for drape and the fabric should make a good big thick border. My original plan was 6" but I'm wondering if something else would be more proportional?

I'm also thinking that in order to get the right framing affect I need mitered corners. I've found several sets of instructions and it doesn't sound too complicated, but I have a question about the math. In all of the formulas you add the length of the pieced quilt plus the width of two borders . . . . But then there's another number added for miter allowance and I've seen numbers from 2" - 10". What number do you use?