Have not carried in NC, but I did start out OC exactly as you mentioned, in an IWB holster. I thought it would be less noticeable, and I believe it is. However, I've come to discover that nobody really notices OWB either, for the most part.
I've pretty much switched over to OWB all the time and said the heck with it, more comfortable (for me, maybe not for someone that notices tho. I don't see the draw time being much different with either mode in OC, but reholstering is probably easier OWB, as mentioned. Lots of variables in holsters, I'm sure you could find a IWB that is easier to reholster than some OWB. There aren't many IWB that have any retention other than friction, that I am aware of, so that may be a consideration.
I never got the what part of the gun you can see being an important thing. You see the same amount of gun whether it is in an IWB or OWB holster, you just see more of the holster OWB, and it is probably more readily identifiable as a firearm when you see all of the holster. IWB at 3:00 can pretty much disappear with the right shirt and holding your arm at your side. If you can't see it, that's concealed. If you don't see it, that's not my fault. Laws in your state may vary. I never got confronted while OC IWB, but maybe no one ever saw it?
Let's say you have an OWB level 9 retention holster where 90 percent of the firearm is covered by safety retention devices. Is that open or concealed. At some point you end up with a Sneaky Pete, which I believe is concealed, yet to me SCREAMS gun. It gets kind of crazy, plus cross state lines and it's almost more than a mere mortal can keep track of!