I seem to have resolved my 9.1.7 issue. Before Apple addressed the malware posing as an Adobe update, I had clicked the "Update" button for what was supposed to be a Flash player update, but instead: a world of hurt and three weeks of troubleshooting. Lucky for me, I live and work with a savvy techgenius, and he was able to spot the nasty bit of code, wreaking havoc but not completely malicious. However the damn thing was trying to take over my camera! Anyway, after disposing of said malware, Logic 9.1.7. running okay, small CPU spikes in one core but nothing I couldn't negotiate. I decided to RotoRooter my MacBook and wiped the OS and reinstalled. Time-consuming but didn't take the three weeks of OSpurgatory.