years ago, I saw Simon Green's presentation, which showed recommendations for FBO performance. The relevant slide is nr.29 from http://http.download.nvidia.com/developer/presentations/2005/GDC/OpenGL_Day/OpenGL_FrameBuffer_Object.pdf .
He recommends to use one FBO and switch between textures.
But then, Valve comes, and tells a very different story. The slides can be found here: https://developer.nvidia.com/sites/d...to%20Linux.pdf the relevant one is nr.65. It says "Do not create a single FBO and then swap out attachments on it."
Now, I realize that (a) nothing replaces doing your own benchmarks (b) Green's slides are years older than Valve's. So, perhaps changes in the hardware caused Green's preferred option to no longer be the fastest one?