Tried to look for it on the internet, but didn't get any concrete answer. Can you use Canon 600EX-RT or Canon 430EX II speedlite on a Canon 5D Mark II (on camera) in high speed sync mode, so that I can potentially shoot with a flash with higher shutter speed, like 1/2000? I'm thinking about whether to purchase a 600EX-RT or a 430EX II. I need it mostly for adding fill light in portrait during bright daylight. So wide open, shallow DOF during the day. Thanks.