Yes the loops mentioned are quite doable in that sort of time frame, but everyone is different. Some like to keep on the move and have an overview of a number of places and others like to visit fewer places and check them out in more depth.
It's quite possible to travel 500-600 miles in a single day but that wouldn't leave time for sight seeing, just basic stops for food and gas etc. As mentioned earlier in the thread, you can get from SF to LA same day using I5, but to explore the wonderful coastal highway [CA1] you really need to allow a couple of days minimum.
