I'm getting serious about dumping my Canon stuff altogether, so I'm looking into flash options for m4/3. I shoot primarily with an E-M1 but also have an E-M5 and GM1, in case that matters. Here are my requirements in descending order of importance. 1.a. and 1.b. share the top spot: 1.a. The flash must do FP Flash (HSS = High Speed Sync in Canon terms). This is crucial since I do most portraits outdoors in bright light and need something that can provide strong fill light with a high shutter speed. I'll likely use 2 flashes on a stand, so power rating of individual flashes isn't a crucial factor although the stronger the better. FP Flash ability is the key. 1.b. The flash solution also has to support off-camera flash whether it be optical or radio-based--no sync cord. If that means additional triggers and receivers then that's not a problem as long as it works. 2. I would prefer the option to use off-camera TTL, but if the only option is manual flash power I'll survive. 3. Also preferable is the ability for the speedlites to hook up to external battery packs, but again not essential. Thanks ahead of time for any help you can send my way.