Graphics, Throttling and Storage Performance
GPU performance is strange here, as it seems HTC is deliberately downclocking the GPU to conserve power. The Google Pixel XL, which uses the same SoC and the same Adreno 530 GPU, achieves 19 percent more performance on average. This margin can jump to as high as 35 percent in some situations, such as in GFXBench's off-screen performance tests. Similar margins were seen when comparing the U Ultra to other Snapdragon 821 devices.
This performance downgrade doesn't see the U Ultra fall significantly behind the pack, and won't have a big effect on current Android games. It's a tight race at times, but the U Ultra does pull ahead of the Exynos-powered Samsung Galaxy S7 in most scenarios to finish 7 percent faster on average. Again, you'll also see a decent jump in performance moving from a device like the HTC One M9.
As expected from the downclocked GPU, the HTC U Ultra doesn't throttle significantly. Long term GPU performance is just 13 percent behind the Pixel XL, a device that throttles its GPU by 13 percent after 30 minutes of GPU-intensive 3D work. The U Ultra can still get quite hot during usage, but at least performance is consistent
The HTC U Ultra produces excellent storage performance for the most part, especially its sequential and random write speeds. This leads to great app loading times and a generally snappy experience, again in line with other top-class smartphones.