The standard rails are 19mm but you can use 15mm rails with the camera (depends on which baseplate you get).
The camera isn't even close to being as heavy as the CineAlta. My red with the ET arri style baseplate, two top mounts, top handle, battery, CF module, red cradle, 18" steel rails on bottom, and 6" CF rails on top weighs just over 16lbs (I just put it on the scale)...Mind you that doesn't include the FF4, the MB20 or the glass (the glass make a huge difference).
As a general note I have an OConnor 1030HD which handles it no problem. BUT on my Cartoni Focus with a Cooke 18-100mm zoom its at the top end of the range for the head (the sticks are the T622/2C which candle close to 100lbs.).
~Marque