I'm testing Corona with the iToo plugins. Corona is really awesome, I'm so glad that you support it!
Forest works as expected, same memory usage as with Vray, but I think I found a bug with RailClone.
It eats memory with each instanced object. So if I have many tiles of a complex geometry source object, memory use is drastic.
When I use point cloud display for RailClone and hit render with Corona, there is the warning dialog popping up "Maximum number of faces reached in RailClone Object. Increase Display -> Limit parameters".
Since I use point cloud, there is no point in this message, other than RailClone is somehow leaking the mesh geometry into memory (or something like that) when the Corona rendering starts.
I have attached a scene file with a highpoly primitive scattered by RailClone, it displays the warning when rendering.
I would love to render my current project with Corona, and there is awesome RailClone stuff going on, so if there's a chance for this problem getting fixed, I'd be very happy.