Sapphire Radeon R9 280X Dual-X been better than my gigabyte
saphire 750khs 1.025v much cooler than Gigabyte R9 280x Rev2
gigabyte cant get voltage below 1.07, hash only 735khs
and my sapphire finds somehow 25% more shares than GIgabyte
Is your Sapphire Dual X stable on that 1.025 voltage with 750kh? I doubt it is. If you flash Gigabyte R9 280x Rev 2 it can get below voltage 1.07 but its not stable. (or i havent find right settings to make it so)
He's not claiming high core clock speed. If the voltage regulators are robust, vDrop is not too steep, ASIC quality is high and the ram is low latency, one can get 750 at such low voltage, yes. Even I managed 750 Kh/s on my shitty VTX3d for a few minutes at core 1050 - 1080 (?), vram 1800, 1.03v