BI: is background (CLI) rendering faster? I had a long (by my standards) render running and got frustrated, decided to do it via the CLI in the background while I work on other stuff.  To my surprise the time per frame seems lower when the render process is invoked via CLI with -b.  This is of course anecdotal, as I didn't take a screenshot before shutting down the GUI render :-)  It also seems to be using the CPU rather than the GPU (maybe user preferences don't carry over to CLI invocations of Blender).  I was wondering which was the most likely reason for it being faster:  rendering w/o the screen updating is more efficient, or maybe my CPU for this particular BI render beats my GPU...
Yes, it doesn't update GUI, so it's faster. I personally always render in cli with -b key anything that takes longer then 20-30 minutes. Additionally it's more reliable and stable than the GUI, especially using an RDP or VNC connection. Sometimes GUI crashes or just hangs on window minimize or monitor goinng off or on screensaver launch. But in background it never happens.