I have absolutely nothing to found this on ... LOL but none the less, I like a long pro taper with a more whippy shaft for two reasons.
The first reason is what I believe, not what I know,

That is, I think that when ever two objects collide there has to be a certain amount of shock and a certain amount of give. Its like a car going over a bump with a shock absorber that gives or a shock absorber that is stiff.
With one that gives, the shock is felt less, with one that is stiff, the shock is transferred more. So, I believe the cue ball is less likely to jump off line with a forgiving whippy shaft. Again this is just what I think, not what I know. But if you think playing pool with a rabbit's foot makes you shoot better and when you have that rabbit's foot you do shoot better, hmmm maybe it matters.
Next is what I know. I like a long pro taper.