It flies - so I imagine that if you attach it to a glider winch and tow it into the air, then allow it to go into a steep dive it may well achieve 3000rpm on the descent, at which point you can measure the voltage reading.
I too had a sluggish starter motor - try keeping it in a damp place and feed
it on lettuce for a few days - you will really notice the difference - but whatever you do keep it away from salt.
It's obvious really if you simply apply some lateral thinking.
