Just a follow-up with a review now that I've used it.
Tokina AT-X 400mm F5.6
Construction: An aluminum barrel makes for a solid, stable lens. I cannot attest to the inside, but it is well finished and appears high-quality.
It has a built-in hood that slides out easily. The tripod mount is solid and can be adjusted out of the way.
Handling: About the size of older 300mm lenses, this is great to use. it can be handheld easily. But at that focal length, a tripod is reccomended, and required when not in bright sun. The internal focusing is quick and smooth, but mine would make a distracting click if it hit the end of the focussing range. The focus ring is recessed in the middle of the lens and can be used manualy easily.
Peformance. I am pleased with the image quality. The colors are vivid and contrasty. I did not have any problems with flare. The bokeh is pleasing especially for closeups where the background really explodes.
One problem appears to be bright highlights that have a purple fringing. This may have just been from water reflections, or it may have been the lens. more testing is required.
One thing i really like about this is the close focus combined with nice bokeh.
examples to follow: