Onebyone

I have the same Brother machine. I use Titanium coated Topstitch needles. They stay sharper much longer when machine quilting then other needles. Aurifil 50wt is 2 ply. I use a size 18/12
Here is the guideline I use:

• 12wt. - 30wt. Threads: 100/16 Needle
• 40wt. Threads: 90/14 Needle
• 50wt. Threads: 80/12 Needle
• 60wt. Threads: 70/10 Needle
• MonoPoly (Invisible monofilament): 70/10 Needle

Here is link to good online information about thread and needles. http://www.superiorthreads.com/education/