I Just had the first run with beta2 and it seems to be much more stable! And it has sound! I can work with fairlight (basics). But the playback with full 4K resolution is still stuttering. I use a nvidia GTX 1080 ti and that should run more smooth (without any node) In proxy mode with half resolution its smooth.
I can work frame by frame without minutes of waiting until the coursor is in the right position.
Maybe that the beta2 can replace the 12.5 - I will go ahead working...