Wide v narrow bars with 42 mm and low trail?
 

I have two low-trail bikes. One is a Terraferma build for long rides and randos, 36 mm trail for 42 mm 650b, and the other is a 1984 Trek 610 with a custom fork giving a 35 mm offset, now using 700x30 mm tires. Arguably that is too much trail, but I like it. The Terra has 44 cm wide VO rando-style bars, and the Trek has 39 cm wide old Ambrosio bars, good old standard road bars - kind of a smaller version of the old Cinelli Model 66. It's pretty comfortable bar, thought better would be a more modern flat-top compact bar, like I have on my Mondonico.

I need to shorten the reach on the Terra, to pull the hoods toward me by about 3 cm. As I ride it, my hands tend to drift that far away from the hoods, so I think the existing reach is too far. I'm tempted to put a narrow compact on it, but ... does a rando-style geometry prefer a wider or narrower bar? I have had a Berthoud bag on the front of the Terra, but it doesn't seem to need the extra leverage of a wide bar. The stability of the bike (tracking straight, holding a curve line, freedom from shimmy) are pretty good, and same for that of the trailed-out Trek 610 with its narrower bars.

I notice older long-distance road bikes, like my 1952 Rudge Aero Special (clone of the Super Lenton so some serious long road time-trialing cred) seem to have been supplied with pretty narrow 38 or 39 cm bars, despite 32 mm tires and trail in the upper 30's and lower 40's. At that time Raleigh had been designing very similar Club-style bikes for long group and solo outings, with presumably similar bars since before WW2.

To make a short answer of a long question.
I think handlebar width - whether road racer, rando, tourer, etc - is a personal preference. (assuming your bags and electronics fit)
I think handlebar shape for long distance riders can be important. Some very new handlebars allow support for wrists and lower forearms, not sure if they are proprietary designs on new bikes. The UCI's rule on prohibited positions in the Pro peloton is what brought 2 new style handlebars to my attention - I have not seen them in use.

I did a 'short and shallow' handlebar swap that improved the ride on one bike. And I went narrower.
And a new build will feature very narrow bars with a flared drop position.

One thing to consider: Will narrower bars provide room for your hands and a Berthoud bag?

The narrower bars will have two future homes: First is my silver Mondonico road bike, which is a go fast and is very happy with a medium saddle bag. For that one the goal is to get a flat top and a compact profile, but it has very quick steering already. It uses 21 mm tubulars.

The other target is either for my Trek 610 which has pretty low trail due to a custom fork, or for my Trek 720 which is nominally a tourer, but is really just going to be (I hope) a comfy long wheelbase cruiser.

I do want a shorter-reach bar for the Terraferma but it does not need to be narrower. I would't complain if I can find a flat top compact in the same wide width.

For your style of riding I can't really say. However I've been use to 38cm wide drops all my cycling life. My previous '91 Paramount re-build I put 42cm bars on and didn't really like them but lived with it for almost 4 years till I got a new bike. My new bike it had 42cm bars too and I still didn't like them. The issue mostly seemed to be that it had me braced too steady. So the natural swaying side to side was absorbed by my arms/shoulders alone. Going back to 38cm bars in combination with a 30mm shorter stem turned out to be the best thing I have so far done for my fit on my new bike. And that bike is the smaller of the split between the two sizes I fell between on the mfr's sizing.

YMMV!

Sorry for the long delay in getting to your response! Your experience sounds like mine in using the narrower bar, that my body moves more flexibly. I also think about this because I'm revising the fit of one of my roadies based on Gordis and Lemond's "Greg LeMond's Complete Book of Bicycling." I'm pretty sure this is what other BF ers have been calling the LeMond Method. Greg wrote that it is what his coach Cyrille Guimard did when he turned professional. Guimard had lead the French national team before that. To confirm the method he enlisted a physiologist Dr. Ginet and an engineer Wilfried Huggi. And itn any case, this is what he decided to teach us in his book. His criteria are about flexibility of the spine and shoulders, and about powerful pedaling -- all sounds right, even to me, returning at nearly 70. But some of my bikes, notably the Terraferma, leave me feeling stiff. The LeMond Method and a 38-ish cm bar should help a lot.

So my Mondonico from 2005 has had its saddle, stem, and bars positioned adjusted per Lemond/Guimard, and my 1952 Rudge is being set up per LeMond, and it will wear its original 38 cm GB "Sylvan Maes" bars it was built with, and my Terraferma has a set of 3t compact and ergonomic bars at 39 cm waiting for it in the Bike Queue, which is in turn waiting for the Broken Lamp, Drippy Toilet Tank, and Squeaky Door Queues. Forgot - the Garage Door Opener and Screen Door Latch Queues as well!