So speed of throw doesn't matter so much as consistency of throw?
Speed is a relative thing, without seeing what you're doing, it's hard to calculate. I assume it takes a little over a second, and perhaps as long as two seconds, to go from the bottom to the top and back to the bottom again.
What ever you do, try and do it exactly the same over and over again. Many use the consistent "tap" method where by the tap at the end of each stroke is the same... be it hard, soft or something in-between, it should be repeatable every time.