So overclock3d posted their performance review of #farcry5. Apparently in this game a Vega 56 is able to almost match the performance of a 1080 FE, possibly in part due to Rapid Packed Math support in the game.
If you don't know what Rapid Packed Math is here is a quote from the review that explains it:
"Rapid Packed Math allows AMD's Vega GPU architecture to offer a 2x performance boost when calculating FP16 math, giving developers the ability to accelerate specific workloads by using less precise… See More
mathematics. If using this kind of math can be done with lower precision with no visual downsides, developers can choose to use FP16 math to reduce memory bandwidth requirements on FP16 compliant hardware and offer a 2x performance boost on Radeon hardware which supports Rapid Packed Math. Rapid Packed Math does not require the use of a low-level API like DX12 or Vulkan, allowing Far Cry 5, a DirectX 11 game, to make use of the feature."
overclock3d.net/reviews/software/far_cry_5_pc_performance_review/1