I'm trying to work with all these things, this is what I did today. With a Sigma 530 Super Flash on the 40d, and the canon 430EX as a slave to the Sigma. I turned of ETTL and set the powers manually. Think the sigma was at 1/8 and the canon at 1/32, but the canon was closer so that would even it up a bit. In fact from shadows looked like the Canon was close enough to have just a bit more power.
No edits yet, just straight of the camera exported/resized with dpp



