sad but true. there is no other/better way to achieve what you want. the bottleneck is the AsVideo node which copies the rendered image from the graphiccard back to the cpu for further processing. this copyprocess is slow in general. you could try with a pci-express card if you haven’T already.
but you should be able to achieve similar effects with shaders in much higher framerates.
yes, FileTextures are stored on the graphic card (with a safety copy in the main memory). The Renderer → Ex9 Texture → Renderer path also stays in the graphic card and is therefore very fast.