In a different situation...
Where I work we have boards (not Arduino) that run from 5V. They have an on-board voltage regulator so the customer can use a higher voltage, or there is a jumper plug (AKA "shunt") to bypass the regulator to run from a 5V supply.
During our tests the regulator is not (supposed to be) bypassed and I run them at about 7V. But, sometimes the jumper is accidentally in the wrong place so the components are "over-voltaged". I've NEVER seen damage from ~2V extra.
However, 12V will ALWAYS kill the RAM, and sometimes one or two other chips.