mining variability

[oddity]

What factors influence mining speed?
If 2 computers have the same card, overclocked to the same rate with the same drivers and the same mining software and settings what are the other factors that can influence performance?

[samr7]

Games and movies also use the GPU, and will take cycles away from the miner.

Some cards will throttle down the clock if the temp is too high, and the fan speed has already been raised to 100%.

If you're mining for a pool, and your pool is being DDoS'd, the miner might become stuck idle waiting for new work.