Information on Cross Vendor GPU SLI support surfaces from GeForce and Radeon | Play3r
DirectX 12 Explicit Multi-GPU Performance Review with Ashes of the Singularity | DirectX 12 Explicit Multi-GPU Performance Review with Ashes of the Singularity | GPU & Displays | OC3D Review
Confirmed: Radeon RX Vega won't get 4-way multi-GPU support in games | PCWorld
What kind of memory management is done in "Multi GPU" that combines multiple GPUs to enhance graphics performance? - GIGAZINE