Hi Ben — I like a lot of setback and I have one of the lugged Nitto seatposts on my Hillborne. If you can justify the cost it is a thing of beauty and should serve you well, though at 27.2 it's only compatible with some Riv frames. And it's steel so make sure to grease it up really well before installing.
I had one of the IRD Wayback seatposts and I couldn't get it to hold tension, (yes, I greased the bolt). It always slid around in the cradle. I found one of the seatposts it's based on, the SR MTE-100. Similar design, comes in a lot of seatpost diameters. They come up on eBay. Mine had a quick release bolt which I replaced with a new bolt and locknut. It's not the most refined looking thing out there but most of it disappears under the saddle.
Here's the one I have on my Appaloosa.