3DMark
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3DMark is the latest version of this hugely-popular synthetic benchmark. Making use of DX11 features such as tessellation, compute shaders and multi-threading, it provides modern-day results and is available as a free download.
Scaling improves as the resolution is increased, topping out at a juicy 81 per cent at 4K. The 6,958-mark score is the highest we've seen from two GPUs.
Examining the logs shows that a single card runs at an average boost speed of 1,100MHz while two cards, due to the extra heat and spatial proximity, ease up to 1,085MHz.