In the interest of preserving the card's longevity, we kept to Sapphire's stock voltage of 1.225V while overclocking and experienced mixed results.
There's not a lot of room to manoeuvre on the GPU core - we managed to bump it up by just 50MHz from 1,150MHz to 1,200MHz - but the card's GDDR5 memory chips don't mind being pushed considerably further. At an effective 6,200MHz, the card's memory remained perfectly stable, though, going beyond that introduced some on-screen artefacts.
The overclock is decent, but even at these frequencies, the Sapphire card isn't a great deal quicker than a Radeon HD 6850 in Aliens vs. Predator at 1080p.