I have not tried either of thoes at such high voltage but I have tried both the HV 306 and HV 510 right at 7.2 volts. Yes, they do work at this voltage, but I find it unnecessary to use them at this voltage because the vapor really just becomes too hot. In my opinion the only thing it would do is weaken the flavor and give you a HOT vapor that is really just unpleasant to me.
Personally running them at 6.4v is the absloute max I would use them at as the vapor production would stay the same at even higher voltages and this would not sacrifice flavor. I usually use my HV801 around 5.5v to 5.8v for a nice cool, flavorful vapor that is thick and satisfying.
But to answer your question in short, they will not blow immeditely as long as you keep them moist but their life will definetly be reduced with the application of higher levels of heat.