I would imagine that if you just touched the end of a bolt with a soldering iron the heat might stay near that end of the bolt. You might not get the whole thing to shift down evenly. Thinking about it, that shouldn’t matter much with any of the older part styles. No clue about the new center though.
What is the stock pulley for MPCNC? Whatever it is, I have no trouble running at 825mm/min with a single flute 1/4in router bit with step downs of 3mm.
380mm/s comes out to 22,800mm/min which seems far too fast for any cnc machine, let alone the MPCNC.