Mac Pro (mid 2010) grinds to a halt when display is rotated to portrait
Solution 1:
This is the sort of thing a well documented bug would let an engineer fix the code to avoid crippling a powerful Mac with a video change.
- https://developer.apple.com/bugreporter/
- Once you have the machine blocked, type
sudo sysdiagnosein terminal and send that output in with the bug report as an attachment. - Usually, you never hear back, but sometimes you'll get an email requesting more details to help engineering isolate the behavior you are seeing.