Here's the skinny: On a maxed out 27 inch 2011 model: under both windows and OSX (only able to confirm frames under windows) Native resolution, vsync on, low effects, no shadows, no clutter, high textures = 60 fps that consistently dips into 30 fps causing a very unsmooth gamely transition. 1920x1080, same settings as above - maintains 60 fps, except In areas of act 3 full party. Drops to 40s or 30s. Conclusion, I can't believe I have to run this game at lower resolutions for it to be playable. Vsync is a must or you are running around with screen tearing the whole time. Solution: new iMac needs to come out or I will likely have to build a gaming system with a thunderbolt capable motherboard.