Which ASUS ROG Strix version? There are two: 11G-Gaming (slower core/boost) and 011G-Gaming (faster core/boost). The 011G-Gaming has the exact same core/boost speed as the standard Zotac AMP! edition when used in OC mode.
With that said, ASUS has a 3-year warranty vs. Zotac's 2-year warranty. I have heard horror stories of people trying to RMA a bad Zotac card, so that right there would steer me away from that brand for a GPU. Especially at such a high level of a GPU. But there's a catch:
The pricing of the two ASUS GPUs, at least in the US on NewEgg, is insane compared to the Zotac at $760. They are asking $999 for the 11G and $1,080 for the 011G. Insanely overpriced, at least on NewEgg. I have not checked elsewhere like Amazon or B&H Photo.