Aurifil 50wt is 2 ply. Connecting Threads is 50wt is 3 ply. I prefer 2 ply for piecing and 3 ply for machine quilting. For 2 ply a universal size 90/14 is too big a needle. I use a 60/8 with Aurifil.
Kas is right. Silk thread will make your machine quilting look like a master quilter stitches. Using silk thread and wool batting is the best way to learn machine quilting.