Quote - Reducing the bounces to 6/6/3 reduced rendertime to 66 mins, and of course puts a limit on the mirror-in-mirror effect.

Still not optimizing Octane correctly I see.  Increase the reflection to 10, because that is mirror reflection.  Reduce the glossy reflections to 4, because you don't need that much depth on the glossy reflections in that scene.  Why would you make them exactly the same as mirror reflections?  Reduce the diffuse bounces to 2.  I've found in most scenes, anything over 2 doesn't have much visual impact on the scene (only in some cases where there is a lot of SSS or translucecy.

This should help increase the results even more.  Every diffuse bounce, and glossy bounce, will exponentially increase the sample convergence.

---

Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.