That is pretty darn good, only 50 fpe loss to the shorter barrel. When Lucky Gunner did their 9mm testing they rated the Ranger 9mm plus p plus as the best in velocity. A little over 1,200 fps with the 127 grain bullet in a 4.22 inch barrel. So, a hot 9 mm is about the same as a 38 Super if you go to the shorter barrel, which was my experience.
Neither Lucky Gunner or BBTI did a study on the 38 Super so there is no direct comparison. Do you have a 4 inch 9 mm with similar ammo? Keep in mind that the Berretta M9 has a 4.7 inch barrel and the Nato standard is a 124 grain bullet at 1,200 fps. So you get into that 45 VS 9mm discussion.
Which is, if you are shooting naked people which is better, the 9mm at 1,200 fps or the 45 at 870 fps?
The next question is, what if the attacker is a 400 pound wild boar? I had one of those nearly run me down while calling turkeys once. I shot him with a 3 inch 12 gauge magnum load, he ran off, never did find him. lol
The Underwood load you tested still has 433 fpe at the muzzle of the shorter gun, that works for me, but I will stay with my 5 inch for woods carry. That extra 50 fpe and 68 fps is going to open up the JHP a little faster and bigger and should give deeper penetration.
All in all, we just decide what works best for us for the anticipated need for that day. For years, my 1911 woods gun was the 400 CB. Since I bought the 10, it goes more than any. That said, unless I go on a trip, there is no bear risk or anything big. My highly accurate 38 Super with the 5 inch barrel and your Underwood ammo is getting 471 fpe, not much cannot be stopped with that, and there are hotter loads on the market. The Buffalo Bore has 3 different loads that get over 500 fpe with the 5 inch barrel.
38 SUPER +P Pistol & Handgun Ammunition
Ironically, now with new powders, it is pretty easy to get nearly 600 fpe with the 40 SW and 155 grain bullets, that game has changed simply because of a couple new powders on the market.
38 SUPER +P Pistol & Handgun Ammunition
Everything we knew about powders and pressures what we could do with this or that round 5-10 years ago has changed, hard to keep up. That said, I may carry a 9 mm around town, but if I think I might need real power, I want a single round hits the first pit bull, wild hog, or armed robber with 357 mag power, about 500 fpe. I can get that in my full size 45, full size 38 Super, a 4 inch 40 or any 10. Just my way of thinking.
I probably spend more time where cell phones do not work, so that is probably why I want that extra power. City people do not really have that risk, so it would not matter to them. It is all academic anyway. Any gun and ammo you have will, probably work. That is why so many people carry the Glick 19, lots of ammo and you just keep shooting until the threat goes away? Right?
I just happen to really enjoy the Super, basically no recoil and hits hard a long way off.