Very good edge to edge sharpness and no vignette for an offbrand lens. You got a good buy there. I'm using a Nikon 80-300mm ED lens. What's the f/stop for your lens at 400mm?
Some excellent action shots on your http://pages.suddenlink.net/jgphoto/index.htm website. What size lens are you using for the surfing images, 500mm? And it's a Canon, right?