[damage]

We could only run that rpm because our dwell time for coil charge was a lot less then what your looking at.
At 8000 rpm the time between firing cycle on wasted spark is 7.5ms in a 4 stroke so if your required dwell time for peak charge is 5ms your coil isn't getting much break. On sequential your firing cycle is 15ms so your duty cycle on the coil is 30%. Also don't forget every time a j gap plug fires you are also removing electrode metal, so in theory your halving your spark plug life too.