I took the 640-3 to the range today! I mostly fired 38 Special as that is what I had the most of that I was willing to shoot, but I also fired a few rounds of 38+P and two cylinders of 357 Magnum. I started with a cylinder of 38 Special to give myself a baseline, then went to 38+P, followed by 357 Magnum. I then went back to 38 Special to finish my session.
The difference in felt recoil between the 38 Special standard pressure and the 38+P was less than I expected, which was reassuring, but HOLY COW the 357 Magnum was indeed a handful! It is great knowing I have the capability of carrying 357 Magnum in such a small revolver, but I think I'll leave my range fun with 357 to my 28-2 Highway Patrolman.
Regardless, I was happy with the feel when firing 38+P. That was something I was never satisfied with when I would shoot my 642, and is why I preferred the few decent options I think are available for 38 Special standard pressure self defense loads when I had the 642. It may not matter much now that I mostly carry 9mm, but as I consider my J-frame as an additional carry option, I wanted to have a revolver I could conceal that would also allow me to fire 38+P more comfortably. Also, while there are some good options in self defense rounds in standard pressure 38 (I like Hornady Critical Defense FTX in this respect), I think the performance and overall availability/range of choice of 38+P self defense rounds is much, much better. All of these reasons went into why I switched from the 642 to 640.
Overall, I expect my new to me 640-3 to be an excellent carry piece!