So, to revive this thread once again, I performed this very experiment this past weekend. I couldn't get a SiN ball in 1 1/6" size, so I settled for 1". Just about all of the game mechanicals seemed to work just fine with the different size. About the only thing that didn't was the rocket kicker.

As compares to the regular PB, this thing has about a third of the mass. It was faaaaaast. So fast that it would blast past the gumball diverter on occasion before it had a chance to open fully. This obviously required a straight, true, and fast hit to the right orbit. It also had a tendency to blow right past the right ramp optos so quickly, they wouldn't detect the balls passage. As I mentioned before, the rocket also had trouble with it, since the ball didn't weight enough to activate the switch for the kicker.

The lighter weight also meant that I was operating in air-ball city. Solid hits to the right ramp also had a tendency to fly off the 270 degree turn and land in the left ramp next to it. One early hit with the upper left flipper sent the ball bouncing off of the rubber post next to the left ramp and over into the gumball machine exit lane.

All of that said, it was still very fun to play with it in there, and oddly enough I seemed to play better with the lighter ball than the regular PB. For instance, I was able to collect the PB jackpot with a shot to the piano during multi-ball which I've very rarely been able to pull off. The black gloss of the SiN ball did make it harder to track, especially since my machine has a GLM door light board with LED flashers going off to contend with. The SiN ball seemed to fare well in the experience as well, with it acquiring no divots, marks, or scratches.

Fun, but I wouldn't leave it in there for regular play, even if I could've found one the right size. SiN balls are also a little over twice the going rate for a OEM power ball as well.

That could be, but I was figuring was that the ball would go through the beam so fast, that the game would not register the passage because the total time of passage wouldn't exceed a timer value.

It's fairly standard practice to debounce switches when working with hardware, at least when it comes to physical switches but it's conceivable one would do the same with an opto switch. What I figure is that the game code doesn't consider an opto to be tripped when the beam is first interrupted, but rather waits for a small amount of time (some amount of milliseconds) before it changes state. Were that the case, the ball going fast enough might enter and exit the beam before that period expires.

That's all supposition though, since I am not TFE.