Does having NM4 gear equipped influence drops in any way?

Some say yes, some say no, can't find official word. Official word?

We don't even have official word on how upgrading gear effects drops. Do drops look at the current or base stats of equipped gear when deciding what can drop?

Although I don't have the link to his post about it, Iamson from Trendy said that it's just gear power that matters, not whether it's nightmare or not.  I don't think the game even tracks if a piece of equipment is "Nightmare" or "Chaos" or whatever else.  Instead, the game just looks at the power of the item.

Of course, he could be mistaken about that, too, and maybe there is a bug that makes nightmare gear not affect your gear drop. If so, the dev team isn't aware of such a thing, though.

His post is... somewhere around here?  He posted it a few days ago I think.  Just run a search on his posts to find it (I gotta get going now).

From what I've seen, only base stats have an effect on loot that drops for you.
That being said, you only think it affect your drops because your NM4 gear is fully upgraded.

The base stats on NM4 items are sub Chaos 3, so many think they affect drops.

Depends on what they converted to. Were they upgraded before or after transition?

If the upgraded stats exceed the stats for the max drops on your tier move to the next tier.

As soon as the drops exceed the gear you have which would be C3 then replace your gear and upgrade the new gear.

The upgraded new gear will influence the drops from then on until you reach the max allowable for that tier, when you should move on.