Ok, so. I got the comp up. If I don’t move around the editor (that uses 100+% CPU just navigating the comp), and run the viewer (once I had the plugins in place), I got the following CPU with Syphon off and on:
Basically, 25% CPU. I suspect you have a module that triggers specific behavior or something out of whack with an old plugin version. FWIW, I saw no OpenGL errors of software fallback.
Let me know if you can narrow this down.