...or (memory) underclock.
Not only am I talking about going below the physical capabilities of the ram chips but some particularly bad core-to-memory clock ratios can erally destabilize the GPUs with symptoms ranging from performance holes, through HW errors, to hard crashes.
I personally believe this rare but repeatable stability loss might be the core reason for AMD imposing the memdiff since the 6xxx generation cards.

I like some of your posts here, Death, especially your touching on the extremely subjective notion of card stability.
How about we formalize (in an informal way ) and shorten some of your stability thresholds:
#define CIS "crash in seconds"
#define CIH "crash in hours"
#define CIW "crash in weeks"
#define CIM "crash in months"
#define CIY "crash in years"       //the holy grail of overclocked mining

I've seen the CIS to CIM delta to range from an astounding 8 MHz (that's a great overclock) to the unimpressive 35 MHz (an XFX 6970 that really pissed me off until I understood its finickyness).