One more schedule? Answered
You did not mention irrigation pipe. This is thinner than schedule 40. That means lighter, cheaper, and less strong. But there may be some uses where the weight and cost are most important. The good news is that irrigation, schedule 40 and schedule 80 all have the same outside diameters, so fittings work on all interchangeably. The difference is the wall thickness, which is why the hole in schedule 40 is bigger than the nominal size. That's so the hole in schedule 80 (thicker wall) is big enough.
Also, way down towards the end, gray pipe is referred to as CPVC. Actually, the gray is electrical conduit, and is colored just to tell it apart from water pipe. It is just PVC, and the same glues used for white pipe work fine on it. If you want a tight 90 degree fitting on conduit, just glue a white elbow onto the gray pipe - no problem.