Below you can see the front-view size comparison of the Fujifilm F600 EXR and Fujifilm Z900EXR. The Fujifilm Z900EXR is clearly the smaller of the two cameras. Its body is 3 mm narrower, 4 mm shorter and 15 mm thinner than the Fujifilm F600 EXR.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.