4x5 can be both smaller and lighter than an RB, oddly enough. My Tech III and older lenses makes a pretty light kit and a Chamonix or Tachihara would be a good two pounds lighter still. And if you like the 6x7 ground glass a 4x5 is just more better, never mind 8x10. But it's much more expensive in terms of film, much more hassle with sheet film and much slower to use, though that last combined with movements adds to its own reward too.