As for the Pillar Ball model I just quickly made it in 3DS Max without caring about unwrapping UVS. That's why you get that awful stretch. I'll be working on having each texture has it's seperate sampler and each shader has it's own constant buffers.
As now it's every mesh has it's own constant buffers. Not every constant buffer is treated equally - bill board shouldn't have the static meshes constant buffer. Foliage shouldn't have the same constant buffer as billboard even know it's the billboard swaying inside the wind direction.
That's it for now.
Octree culling always sounded to me as a bit of overkill.
As far as I know there isn't much "verticality" on games in general, and you're making all queries more complex just for that weird case where you're looking straight down or straight up and nothing is seen.
But thats just my armchair opinion. Haven't measured differences precisely.