Shooting HSS with speedlites will diminish the power. This is where you need something more powerful like a strobe. Even when you shoot HSS with strobes, the power will drop but since the strobes are more powerful, it can still produce enough light in the daytime. Also if you are using speedlites during the daytime, it can help if you place the lights closer to the skater. So perhaps shooting fisheye can help since you are pretty close to the skater anyways. You can also just buy another flash and buy a bracket that holds them together to emit one powerful flash.