After researching this is what I think. Please confirm or correct me:

Both have the endurance package?
MIM parts began with -5?
Main MIM parts are hammer without the firing pin and both the hammer and trigger are not hardened as in -4’s?
Do some -5’s have the hammer & trigger as the -4’s?

Anything else one should know if deciding between the two?

Are all -4 and -5 629 Power Ports drilled & tapped?

Many thanks!

Looks like you have it figured out. I would prefer a dash 4 but would not hesitate to buy a dash 5 if one presented itself. The MIM parts do not bother me. No dash 5s have any old dash 4 parts but I bet it would be possible to find a very late dash 4 that could have a MIM trigger. This was done on the model 29-6 from the same time period.

All the 4s and 5s should be drilled and tapped, you can tell by opening the cylinder and looking at the frame underneath the sight

1.) Yes. The endurance package was introduced as dash 2E.
2.) Yes, except the triggers are interchangeable and S&W started using MIM triggers in some models while they still had the older frames.
3.) Yes for the first half then no for the second half. Forged hammers and triggers were not through hardened. They were case hardened. While it has been posted here that a thicker layer of their surface is hardened I'm not sure about MIM hammers and triggers.
4.) MIM hammers usually do not include a firing pin so they do not fit in dash-4 frames. Older style hammers with a pivoting firing pin do not fit in dash 5 frames. It used to be true that all forged hammers included a firing pin and all MIM hammers did not.
5.) (regarding the power port revolvers) The only dash 4 and dash 5 629s that are not drilled and tapped for optics would be fixed sighted revolvers if there are any.

I like the appearance of forged hammers and triggers and after my eye sight diminishes in old age I might want to put optics on my longer barreled 629s so for longer barrels my first choice is dash 4. Since I prefer flash chromed hammers and triggers and I'll never put optics on snubs my first choice for snubs is dash 3. That's theory. An individual 629's action, especially early carry up, usually is more important than its dash number. The exception would be long range accuracy. To pursue bench rest shooting or silhouette matches I'd insist on the endurance package for its tighter cylinder throats and smaller forcing cone. I actually bought 629s I found at good prices. If price does does not matter pick a dash number after evaluating which features are most important to you.

Thanks for your replies!

I have two of the 629-5 models. One has the 5" barrel and the other has the 6.5" Nice guns. They shoot really well.

I’m the new owner of a 629-5 Power Port that I believe spent much of its life in the safe.

Swapped a Thunderbird for an Edsel??