Upgraded to Yosemite on my 5,1 Mac Pro and the UI lags hard, particularly when safari is open. All the windows and any video running seems to freeze, but my mouse cursor still moves and any audio plays fine while the UI is frozen. Graphics card is a AMD Radeon HD 7950 with two 23" Apple Cinema Displays. Tried this but didnt seem to help: Any other ideas? Thanks in advance.