works stable - if you don't do a lot of changes while the render viewport engine is on
but one issue - the 3dmax viewport is a lot more slower, it's choppy, takes a lot more to select and rotate around when rendering..
when turned off it's fine.. using directlight (now saving with 3200x3200 px before with 800x800 it was the same)
I am in the middle of doing a project and I am using the 2013 now until I finish it, since it's as stable and usable as 2012 version,
only the viewport issue - anyone else got that problem - the scene has 13 000 polys, real small, same scene in v 2012 3dmax viewport performs better..
..and there are no material previews of anything, maps and textures are all black - I've gotten used to it so I't would be a great surprise if it started working

loaded the scene saved from 2012 though
Also - I hate the HDRI environment workflow, I don't even want to test something with it since its a bit of a pain in the ass compared to octane standalone..
it should be connected to the Octane daylight object - just put a load texture box and sliders from octane..