I have only been at this a relatively short time (5 years) but so far my observation has been that shafts that are going to stay straight never seem to be warped at any time during the cutting down process. If a shaft is warped after the first cut and then again after the next one it's probably time to put it in bin "B" even if it's still .700" or larger. The ones that are straight every time can be cut down to size relatively quickly from whatever size they are currently at with high confidence if you've already cut them more than once.
That's what I've noticed anyway. I have tried cutting these straight shafts extremely fast for my own players as experimentation and they don't seem to warp. I mean from .650 to playing with them in a few days. The good wood seems to stay straight and the warpers can't be trusted ever. Fortunately most good maple is in the first category but some that looks excellent just won't stay straight. Maybe cutting them super slow can save some marginal ones but I wouldn't count on it.
JC
Try letting them experience 100* at 10%.
They will move.
Season and cut a bunch down to .525 ends.
Check them a few weeks after summer and winter .
The good ones will go back straight if they moved at all during summer and winter . Assuming your storage for them is semi-controlled.
If you control the temp to 75* and humidity to around 45-50%, they probably wouldn't move.
On that note, never buy tapered shafts if you can help it.
The center holes on those were decided for you.
You should decide where the centers of your dowels should be.
It's hard work taking squares to rounds then parting the ends and centering the tapered pieces right. I don't bother coning these days . They are a waste of time to me. What matters more is right centering . A correctly centerd .650" tapered pieces are more stable than badly centered .750" cones in my experience. If I need to get rid of the bad guys ( grains that have no function but to fight the other good guys ), I whack them.
Needless to say, use thin kerf wingers that are sharp.
Never use thick straight cutters. Too much stress on the wood.