While no longer the flagship SoC from Qualcomm, the Snapdragon 821 is still a very capable mobile platform with particularly strong graphics performance. However, the 821 was still using only a quad-core CPU design, which has been supplanted with an 8-core design with the new Snapdragon 835. In the CPU benchmarks this should give the 8-core Kirin 960 in the Huawei Mate 9 an advantage in multi-core results.
We will first look at results with Geekbench:
Single-threaded performance is Apple's strongest area with their A-series SoCs, and while the Snapdragon 821 performs well it is clearly showing its generational disadvantage in the CPU department.
Next we will look at GPU performance, and here the story is quite different:
In the GFXBench tests the Snapdragon 821's Adreno 530 graphics prove to be quite potent, though Apple's A10 Fusion did score a win with the ALU 2 test.
Finally, a look at a couple of 3DMark benchmarks, with both standard (OpenGL ES 3.0) and extreme (OpenGL ES 3.1) versions of the Sling Shot benchmark. Note the absense of the iPhone 7 in the latter test, as Apple does not support OpenGL ES 3.1, opting instead for their own 'Metal' API.
Once again the Snapdragon 821's Adreno 530 graphics look pretty strong, and combined with the good (not great) CPU numbers the Pixel sits somewhere just out of the high-end of the current market now that phones like the Samsung Galaxy S8 (Snapdragon 835) have been released.