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It might be interesting to investigate what combination of ignition and exhaust valve timing defines the limits before there would be a possibility of the firing cylinder trying to turn the engine backwards.
If the ignition and exhaust timing were never such that the pressure in the firing cylinder exceeded that in the exhaust cylinder until the direction was decided, it would be OK with 4.
As a rule of thumb, ignition timing is typically set so that the maximum pressure in the cylinder is achieved about 10 degrees past TDC, ignition advance from 30 to 0 degrees BTDC. Not sure if that's enough info. to allow some thought about it.
I'll have to think about when the crankshaft speed is greatest. If it's not at a minimum at TDC/BDC then the engine should keep turning. The crank doesn't stop with the pistons and will have a peak speed as many times as there are cylinders but I'm not sure what the angular disposition is.
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