Matt, thanks for your website. Currently, I'm gravitating towards the Sigma EF 530 Super.
While reading about the HSS feature, I found that your explanation did not really indicate
why I would use this feature. Under what circumstances would you want to fire faster than 1/180s with flash?
Pentax P-TTL Flash Comparison: High-Speed Sync
Hopefully, at a later stage you be able to include an animated diagram of the the front & rear shutter curtains in action, and shots taken with & without various flash features.
Dan.