Aurifil is 50 wt 2 ply. CT 50 wt is 3 ply. That is the difference.
You need a 90/14 size needle for 3 ply 50 wt. thread. The CT Pro on the cone is 70wt poly which is great for bobbins and machine quilting. I use topstitch titanium needles from Superior for all my machines. The eyes is longer and makes a big difference. The titanium needles stay sharp almost forever.