Old with a reasonable memory.

There is one more factor in this discussion that hasn't been fully brought up yet. And that is where the transition on the steerer where the threads start compared to where the top of the head tube is located. Ideally the threads start right at the top of the head tube so that the expander bolt on the stem will be below the threads. As already mentioned the expander can possibly bulge the steerer in the area where the threads are located since there is less material there.

For example on the frame Skip made in my class, we chose a steerer that its length placed the transition just a little higher than the top of the head tube. Then Skp cut a bit off the bottom so where the threads started was right at the top of the head tube. This is one of those refinements custom builders can do to help future proof the frame to future fittings. This way when the stem needs to be raised (as the rider ages), it is not in danger of the expander bolt getting in the threaded area.

Cable stop
 

Interesting discussion. My first question: can I have the cable stop? Kidding. Love all the pics in the thread and the signature on your bike. Oh yeah, my opinion: spacer. It's the simplest.