Testing with 100mhz scope revealed no discernable glitches on the port pin.

Saturation is fine (.2 volts or so)

The circuit is grounded emitter, with 4.7K pullup. I'm not sure when you mean by better performance, noise immunity, switching speed...? what? I'll hack the circuit a little and see if it changes.

The series resistor was experimental to see if I could change the behavior.

The design is done or I'd switch to another opto.

BTW what did you use to make your little sketch? I need a good generic graphics program.

BTW, I used to be in the laser cutting / robotics business. It was a fun technology.

Thanks for the help guys.

Bob Bailey