Perfesser, I don't think it makes much difference. We're talking a 2" barrel at very close ranges.
Unfortunately, the actual shootings I have knowledge of/experience with only include one J frame; that was inside a car, dope buy gone bad, and our guy used an M-38 with Glaser Safety Slugs (old ones; this was in the early 80s). He's on here at times, maybe he will see this and chime in.
As I recall, the performance of these were not too impressive, but our guy walked away from it and the bad guy went to the hospital, so I guess they worked well enough.
I have been carrying a J frame of one sort or another, for back-up/off duty (and occasionally primary) use for almost 30 years. I have always leaned toward the old FBI load; a 158gr lead SWCHP; because it has good history. The reports on the CCI 135gr "short-barrel load" have been mainly positive, and it does indeed have less muzzle flash than anything else I've tried; to include that 125gr standard pressure NyClad that we all loved ten years ago.
That Gold Dot 135gr +P .38 is what I have been carrying for a couple of years now. I feel no pressing need to change, so that's why I haven't made the effort to procure any of the new NyClad stuff. But I WILL get some eventually; especially since they're making it in 158 trim now. I hadn't heard that.
Again, while ammunition selection is an important topic, I personally just do not give it much thought when these belly guns are concerned. Hell, I remember back when a Speer 148gr hollow base wadcutter, loaded backwards in the case over five grains of Red Dot powder, was considered "the shiznit" for a Cheif's Special...
"You say you have a "sheepdog" mentality. But if you have no structured training behind you... you're just barking."
"The retard cannot comprehend that everyone else... isn't."