Asobinet has published this precise size comparison. What immediately stands out is that the new Sony RX1rIII is 1.5 cm deeper. That’s quite a big jump. The body itself is thicker, probably to make room for all the new processor chips and for better heat management. The lens itself also appears to be a little bit longer.
Would have loved if Sony engineers would have found a “trick” to add at least in lens stabilization without to compromise the size too much. That is my major complaint a part of the obviously high price tag.
Sony RX1rIII preorders at BHphoto, Amazon, Adorama, Fotokoch, Fotoerhardt, Calumet, WexUK.