I'm sorry, but what's your point?
[/quote
My, aren't you cranky! Perhaps you're not familiar with the idiom here... folks, like you, ask for help... other people out of the goodness of their heart offer assistance. That is not well-supported by the original poster (that's you in this case) responding intemperately to those attempts to assist. Perhaps it's a bad day, we all have them.
My A&P/IA was right. He usually is, so I trust him.
So... why are YOU here?
Your original question was, "Is there any measurable way to determine if a starter is spinning the engine fast enough?" The answer is yes... I referred you to S-Tec's troubleshooting chart. Essentially, if you see 10 volts at the starter while it's cranking, then you're getting what you need for it to perform.
OTOH, if there's either electrical resistance problems external to the starter, or high current draw issues with the starter, the voltage will be lower... and you'll know you are NOT getting enough energy to/from the starter, and need to remedy the issue. The troubleshooting chart goes on to describe how you narrow down the nexus of difficulty.
But feel free to stop reading at any point! However... I'd encourage you to be pleasant when asking others for assistance. Things go SO much more smoothly that way!