Be realistic about the working distances you expect. AA-powered flashes are very limited in modest sunlight unless you're shooting REAL close. Could be the same with LED lights...you'll have to see.

A few years ago, I was shooting an amateur bike race. I wanted to experiment with lighting, as I was merely shooting "for myself". I had four 580EX IIs, two battery packs, my usual gels, two stands, and enough Mini/Flex PocketWizards to have fun. I was shooting a mile-long hill climb, and sat uphill of the spot I wanted to shoot. I put a 580 on top of the first stand with a battery pack, no gel, about head-high. I clamped a second 580 low on the stand, maybe 1' off the ground, aimed it up towards head-high, and gave it a 1/4CTO gel. I put this about 10' downhill from me, aimed at a "spot" on the street about 20' downhill from me assuming the bikes were riding on the yellow stripe. I made a second rig in the same fashion, put it about 20' downhill from me, and aimed it at a "spot" on the street about 30' downhill. This gave me a longer box of light to work with, but since I wasn't shooting from between the lights, I had to mentally time the shot through the viewfinder to be in the box.

I was shooting with a 1D3 and 70-200/2.8 IS, with a PW Mini on top, and the AC3 Zone Controller. The high flashes were group A, and the low flashes were group B. I put a 7D with 16-35 on a mini-tripod near the ground, about 5' downhill from me, on a PW Flex, in group C. I could enable/disable any group from atop my camera. I knew I was shooting at a time when the sun would be rising at my 7 o'clock position (lighting the riders' front left), so I was trying to fill in the right side. I have one good sample from the day:

First, the teaser shot, from the 7D/16-35, without any help from flash. This was remotely fired either milliseconds before or after the main shot, not sure which (full size at http://www.flickr.com/photos/alibear...7632794051121/)
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Next, the lit shot, from the 1D3/70-200, courtesy of two or four 580s working "beyond" their limits, courtesy of the fantastic high-speed syncing tricks of the PWs. I was shooting aperture-priority but managing aperture/ISO to keep the shutter speed as close to 1/1000th as possible, as that's the optimum hypersync speed for that body (full size at http://www.flickr.com/photos/alibear...7632794051121/)
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No, I didn't black out the background in Photoshop, whatsoever. That's shooting from a more level angle against a rock wall that wasn't getting any sun, and the flashes were lighting the rider's right side.

I wrote all of this to say that what you see here was at the outer limits of AA flash. They got hot that day, they needed multiple battery/battery-pack changes during the day, and my results were average to abysmal. This was one of the best examples I got all day.