Regarding Kepler vs Fermi. Yes, the Fermi was a bit faster (I did use the 580 before I bought the 680). But if I can't get the scenes into Octane, it is of nu use to me at all

And the village Courtyard exactly shows the problem.

It has multiple parts. Each part has its texture, its bump map and many of them (plants) transmaps. All transmaps and bump maps are greyscale - so you can have a max of 32 on the 580 (and 72 on the 680), so you are running out of slots here.

In this case you can render it without the bump maps. Go to the material editor, right click on the scene line and select remove bump maps. You will see that 600 something bump maps (actually references) are removed. Now the image statistics say you only use 10 grayscale maps and you can render it

The limit refers to unique textures (so many references to 1 map counts as 1). Stonemason uses for each prop a different map. In this case it is a problem since there are just too many maps