Using the Vivitar 283 with the VP-1

I'm using Vivitar 283's with the Vari-Power 1 to photograph hummingbirds. Does anybody have or know of a chart that shows the flash duration at the various settings on the VP-1?
I've been using the Vp-1 set to 1/16th, but it's not totally freezing the motion of the wings.

http://www.rpphoto.com/howto/hummer/humguide1.asp

http://krebsmicro.com/VIV283/index.html

i once had a tutorial on stop motion using a 283 n it rated duration from 1\2000 to 1\30000