I went to the range this morning and fired Speer Gold Dot 38 spec. 135gr + P alongside DoubleTap 38 special Match 148gr Hardcast Wadcutter in my wife's S&W M638.
I also fired the Speer Gold Dot 38 spec. 135gr + P in her M64 & my M65.
Unfortunately it was so cloudy and dark that I could not get one chronograph reading. An 'error" messages each shot. I did shoot some groups and was able to compare recoil between the two so I thought I would report.
As you can see in the pictures below they both shot pretty much POA/POI in all three revolvers. Groups are all similar and could be better with some practice. I rarely shoot these revolvers and it shows.
In the M638 the DoubleTap recoil was mild compare to the Speer. I thought both were manageable, both reasonably accurate. (Notice I got two bullets in one hole with the Speer in the M638) I'm sure that regular wadcutters like the Federal Match would recoil less and I'll try some once I find them at a decent price.
It seemed the Speer Gold Dot 38 spec. 135gr + P was just made for the M64. Soft shooting & accurate! A joy to shoot! It did OK in the M65 as well. Thanks to all who recommended it to me!
So the verdict is: For now will use the DoubleTap in the M638 snubby and the Gold Dot in the M64 for a long time to come!