One of my bolts is parkerized and one has Cerakote Elite, which is thinner than regular Cerakote. The Parkerized bolt is very slick. Feels like oiled glass. Parkerizing holds oil really well. So I have a light film on the bolt. The Cerakote Elite bolt is a bit stickier, but I don't really notice it in the moment, while shooting. But if you sit there and play with it, sure you can feel it's not as slick as my other one.
I'm really happy with the parkerizing. You don't have to worry about sending off to a third party for DLC or whatever. Most smiths can do it themselves in their shop. And the way my smith did it, it's a dark grey color. And with a little oil, it turns black to match the graphite black Cerakote of the action.
I will parkerize every bolt going forward. It also doesn't add much in the way of surface material, so tolerances stay the same.