When I take the effort to carry a longer barrel, I might as well get better performance out of it as a pay off, no? 147 HST gets less velocity in my 92 compact than in my diminutive Glock 43. That's not to say that it wouldn't perform well, I guess I just feel like I'm getting ripped off.
On the other hand, the 124 Gold Dot seems to take full advantage of the additional barrel length.
This wasn't meant to be a Gold Dot vs HST comparison, rather a 124 +P versus 147 comparison, and how they perform differently with different types of guns and barrel lengths. It just so happens these are the two I keep on hand.
As for the Gold Dot, did a bunch of testing years ago with different mediums and the 124 +P Gold Dots performed the best for me. So I bought a bunch (still have the older style gold/brown boxes). It should be noted, this was done prior to HSTs were around (either created, well known, or widely available as far as I knew at the time).
When I got my P938, I decided I wanted to keep a non +P round on hand. Admittedly, I didn't do my own tests, but did a lot of research and watched the ammo quest short barrel 9mm performance videos. The 147 HST seemed to work the best, and were readily available, so that's what I got.