One of the advantages of using the X double buffer extension or XRender or something like that is you don't need to send raster image data over the network. You

One of the advantages of using the X double buffer extension or XRender or something like that is you don't need to send raster image data over the network. You're still sending ordinary drawing commands, and it's the server that accumulates the results into a pixmap somewhere. If it is slow for you, you can turn off the new stuff: (modify-frame-parameters nil '((inhibit-double-buffering . t)))