Octane has micropoly displacements which was the one I referred to with the big slow down.
The octane grass sample scene has micropoly displacement. Its good for bermuda grass like vray micropoly displacement. Sadly we don't have that in native lightwave.
If you're going to use displacements for mountains I think its better to use native lw displacements. They're not micropoly displacements so you won't get super fine detail like the micropoly displacement in octane. But it will render fast and no render time hit afaik.