From what I understand, the theory is that a straight up draw is faster because the barrel doesnt have to rotate as far forward to quickly come to a horizontal (ie firing) position.
Yeppers. If you look at some of the Open class "race rigs" in IPSC competition (like the Ghost Holster:
http://www.ghostholster.com/), they actually cant them barrel-forward...for that very muzzle-to-target travel distance. 'Course, they also let the holsters ride lower than is IDPA legal.
With a high-riding conceal holster, I actually like a 15-degree FBI cant. It just seems easier for me to accurately get to the gun under clothing that way. And besides, I won't have to worry about an extra three-tenths of a second in delay of presentation time affecting my scores for a
long time.

Reloading mistakes mess me up far more than getting the gun out of the holster.
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