DR is such a subjective thing. their 13 stop number is a lab based number. I can't really say yet because they are still working on the sensor calibration and that's what affects noise a lot. Noise affects the DR.
My experince says it's not quite as good as an Alexa but it's pretty close, and it's way better than a 5Dmk2. I shot some side by sides and it was chalk and cheese.
jb
Admittedly, I hope they can ek out every bit of that measurement. 13 usable stops would be pretty perfect.