The iPads and MacBook Pros have those "variable refresh rate" displays. I haven't seen any information about the new iMacs yet. I fear that Apple only cares about this feature in respect to battery life on laptops and iDevices. But variable refresh rates also improve the fluidity of games (and possibly videos). The Radeon cards of the iMacs support FreeSync, which should hopefully work on Windows and on an external monitor, at least. Anyone who gets a new iMac can report on this issue.