Not sure what happened with Anandtech, perhaps a MPC limitation? Need more information to make an assessment.
The IvyBridge driver does support 4K for AVC, and 4Kx2K for MVC. The support is reflected in the MediaSDK 2012 R2 release, with a current 15.26 IVY bridge driver. Support for additional decoders and encoders is currently being discussed.