My game went all slow so I did some simple profiling and well, it's really CPU bound
and it seemed that the Terrain node ate most of the CPU (I have several terrains visible ingame).
First I tried (stupidly) to use VBO but as the terrain optimizes itself each frame that was no good so I wrote a 'fixed' (as in 'not changing')
terrain class that works about the same as the original one (but with VBO) so I though I'd share it here.
BTW my game went from ~15fps to 150+ so for me it was the right thing to do

MSVC project (Windows exe included that shows original and new terrain).