Even the real Arduinos face potential voltage regulator failure at higher voltages, they have even lowered the specs over the years because of this... Mind the regulators specifications (they will vary by manufacture) and consider the fact that they have little to no heat sink, so the higher the voltage the sooner they will overheat... 7-9V is what I would recommend in most cases and if you want those little stick on heat sinks will help keep the regulators much happier, space permitting... That or jumper the regulator and use a regulated 5V input...