Across the board off the graphics settings the performance is horrible right now preview or no preview.
I am running W10 which isn't really the problem because it is already functioning normally on everything else including UE4 editor.
Performance is dropping all the time and I think I crossed 40fps once on low and then it dipped down to 20. Anything higher than low and it has massive freezes of 2-3 seconds
But its an alpha and I hope you use all the feedback from here
My system includes an i5, 280x, 2 SSDs and 16GB ram