scombs get bolder with size.
about the sudden death thing, let's say once they are approx. 7-8" long, they are powerful enough in a full throttle dash to kill themselves if crash into glass/rock/branch. that's my theory anyways, it's what happened to my tats, many of them.
if you do get the scomb, give it a bit of cover, might keep it from being skiddish.