The photo quality from both cameras are equal.
There are many complaints about the video images from the Casio Z850. The Z750 video is much better.
The Z850 has manual controls in addition to the normal auto controls, the SD600 does not.
Other than that, it is a toss-up.
I am going to buy a camera for a trip in New Mexico. Most of the shots will be outside and will probably be roughly handled. I was trying to decide between two cameras that have good offsetting features from each other. Please help in this difficult decision.