RE: stuffing tube
Beboppin,
Out of curiosty...why/how did you start the practice of "nicking & roughening up" your flex shaft?!
Anyhow, your flex cable is made from braided metal strands. Nicking and roughening them up will at the least, make the flexshaft weaker (bad @25000 RPMS - you are asking for to fly apart on you) - and "nicking" is likely resulting your breaking some of these strands.
The reason it seems "smoother" to you is because you are wearing out the factory diameter of the flex shaft (its not fitting as snugly in the stuffing tube as it did when it came from the factory). This "play" you are creating is going to lead to your wearing out both the flex shaft AND the stuffing tube prematurely.
That sound about right everyone?