Someone recently posted a schematic of a RCexl CDI unit in this thread here:
http://www.rcuniverse.com/forum/m_11114518/tm.htm
So trying to use more than 6.0v would cause excess current consumption and cause something to overheat and fail. They aren't using heat sinks inside and the tiny suface mount voltage regulator for the microprocessor is only rated to a max of 100ma too. I would bet that the voltage multiplier circuit transistors would be the failure point, but the little HT7550 voltage regulator is not going to like a higher input voltage either. But even the trigger SCR could go out of spec if the input voltage is too high.
It would be interesting to know what the output voltage is on the voltage multiplier that drives the ignition coil primary windings is.
A good hint though is the datasheet for the X0405ME SCR is 200 to 800 volts, max current 4amps. Thus the circuit is tuned for turning 5v into at least 200v to drive the coil with.
