My open road rides are definitely faster than the Neuse because it never fails that I wind up behind a bunch of people and spend appreciable time during the ride going 5mph around people. Or take the corners easy.
I've done 20mph on a 60mi loop around Falls lake by myself that averages about 50ft per mile elevation. I've basically done the in-town 60 ft per mile A-group ride at over 20 with all the stop signs and lights and getting back up to speed. I say that as lately it feels like I pull a lot, am off the front over the hills, or whatever.
I can't get speeds up in Umstead because I basically take parts of the bottom of Turkey in the corners at like 5mph. Scared of sliding out or meeting somebody head-on. I'm taking the big G2G and other downhills quicker. I think recently I almost broke 20mph on the westbound G2G.
I'd bet Samson for a single lap of the big-loop including Turkey would average in mid to upper 200's for most of that route, for 45min. Like, probably 250 to 260w overall average and maybe 280w NP. You ride that route a LOT and from what it appears, you often ride it pretty hard with good handling skills. And have done it for years now.