Conclusion for those who find it too long a read.
"What it means
In short, chips throttle, but the 810 throttles more than most, and it's severe enough that the 810 is actually slower than the 801 or 805 in some CPU-bound tasks over the long haul. The Exynos 7 Octa, which has similar specs on paper, is much better in practice.
At this point, Qualcomm has implied to us several times that its use of ARM Cortex CPU cores was a stopgap measure—Apple got the 64-bit A7 chip to market around a year before anyone expected it to. Chips are designed over a period of two or three years, so using the ready-made Cortex cores were the quickest way to get a 64-bit response to market.
The results, unfortunately, don’t look great. It might be because the 810 is using a 20nm TSMC manufacturing process instead of the 14nm Samsung process used for the Exynos, or it might be that Samsung has more experience working Cortex CPU cores into its designs. Whatever the reason, our testing of real phones with these SoCs in them shows that 810-based phones are slower and have worse battery life.
Qualcomm's next major flagship is the Snapdragon 820, the first to use its custom-designed 64-bit “Kryo” architecture. Rumor has it that the chip will be made on the same 14nm Samsung process as the Exynos 7 Octa.
A return to its own CPU cores plus a newer manufacturing process should hopefully mean a return to the kind of performance and battery life we’ve gotten from Qualcomm-based phones in years past. All signs point to the 810 being a one-time slip-up and not the start of a trend—let’s hope that those signs are accurate."

