Rule: Sync speed is the fastest shutter speed you can use with flash, period.
The 5D's flash sync speed is 1/200. At a recent wedding just before packing up, I tried experimenting with my cam's sync speed by setting it to 1/500.

I then asked our assistant Archie to illuminate one side of his face with a flashlight. Here's the result:

Tech specs:
Canon 5D 1/500 f/4 ISO 800
Then we grabbed Jay and Gracious for one last portrait before we called it a day:

Canon 5D 1/500 f/2.5 ISO 1600
Interested in offcam lighting? Know the rules from sites such as Strobist and FlashFlavor.

i like it! it's cool! =)
hi archie!!!! :)
@ Neva: Aloha! yahoo im the feature presentation haha! :P
strobist na to!
Fun Stuff!
Hi. How do you set the the shutter above it's max flash sync speed? I have a 40D which has a max flash sync of 1/250. In manual shooting mode with a 430ex, the camera seems to cap the shutter speed at 1/250? Thanks and awesome photos!
Hi Elmo, I triggered the flash with a pocket wizard.
I don't think it will work with ettl flashes, unless there is a custom function that I'm not aware of. It would work if you were using a 3rd party manual flash such as sunpaks. Or you were triggering strobes using the sync cord.
Definitely will play around with this. PW's are quite expensive but we just ordered an Elinchrom Skyport set - a cheaper alternative. We'll see how that goes. Thanks for the response.