I just installed v4. I loaded something up and sliced it and it went out to lunch for a while. When it came back and showed the sliced gcode, I tried to move around the object. It crawls! So, I loaded up v3.1.1 and it came up with the same objects loaded. So I sliced it and navigating in the gcode viewer is very smooth. I tried several objects with similar results.
Is v4 a huge step backwards in performance?