These two tests belong together. It would seem that inlining a (sprite-local) custom block does not speed things up ... UNLESS it's under an event hat that is being broadcasted to frequently.
However, this not a safe conclusion because it's not clear that the two options produce identical visual output. The animation produced in Broadcast Short is noticeably choppy. The shorter execution time may be because Snap! is actually dropping frames. Or, it is rendering them faster than humans can perceive -- in which case it is a valid result.