Jdubs,
I think the loss in speed is attributed the idea that the string, when released, actually falls faster than the tubing, thus the string actually pulls the tubing along creating a small amount of drag on the string. I would say however, that 12 fps would probably be the extreme. I myself do not use tubing, but I make sure to draw every time I enter a stand ensuring the peep comes around full. It's definately not a sure fire thing though, I'm sure someday it will bite me in the rear.
CRITR