After leaving the slab from Cut #3 suspended in the air, I came back the next morning to find that it had fallen back in the water at some point. The lag bolts had come loose, which is now another wrinkle to iron out.
I decided to approach cut #4 with a different strategy, cutting a long and narrow chunk of ice hoping that it would sink into the bottom of the pond, relieving the load put on the lag bolts while waiting for everything to re-freeze. I don't have video of this because I filmed from the beginning and this piece took twice as long to cut, so my memory card filled up at some point during the process. I was able to get the piece of ice almost 9 feet out of the water, but the locking mechanism had failed after Cut #3, and the winch free-wheeled back down, ultimately breaking the slab. But a small chunk remained, so I left the rig hooked up to see what happens over night.
The slab broke into several pieces, and I took some interesting photos of the various chunks interacting with each other. I slid one piece under the remaining slab still attached to the line, and got some strange 2D and 3D effects happening under the water, which really gets at an 'other' space.