[WORK-AROUND]
To anyone else who runs into this problem.
The only way I have found to fix Premiere Pro CS5’s ultra slowdown issue is as follows:
1. Create a new Project with the same settings as your current project.
2. Copy & Paste all files and clips from the old project into the new project.
This includes all files in the Project window and all clips in the timeline.
Thankfully when you copy (Ctrl + C) it keeps everything in the clipboard even after closing the old project and opening the new.
After I did this the UI was lighting fast again.
This proves updating to the latest version of CS5 does not solve the problem. It’s a pain in the butt to have to do go through this process every so many saves, but at least it restores your project into a fresh new file.
Adobe, please fix this bug for CS5 users!
ShaneNewville.com