The size of the needle you use is determined by the weight of the thread you are sewing with. The hole and the grove at the front of the needle need to be large enough to comfortably handle the thread, but not so large as to make unnecessarily large holes in the fabric that the finer thread won't fill.
Sally Collins makes small and miniature quilts and would use a very fine thread. I'm not sure what brand/weight thread she uses, but it would stand to reason that when making miniature quilts you need the absolute least amount of bulk in every seam allowance. Thus...she will use a very fine thread (probably a 60 weight or a silk 100 weight) and a very fine (size 60 or 70) needle.
I use a size 60 or 70 needle when using MonoPoly and size 80 when using MasterPiece.
Check the Superior web site for information about what size needle to use with each kind of Superior thread:
http://www.superiorthreads.com/shop/category/home-machines/products/
Hope that helps.