100-400: Does microadjustment improve the 'not-good' copies?

I've heard about Liquidstone's test of similar sharpness at f/5.6 and f/8 for the 'good' copies of this lens. However from the outlets where we have to buy, such testing may not always be possible.

So, my question is can focus microadjustment do something for those lenses not as sharp at f/5.6 as at f/8? Is the sharpness of f/8 reached at f/5.6 after microadjustment?

Also, what are the chances of getting a less sharp copy among post-2006 100-400 s?

Aware of the 400/5.6 prime, but afraid it won't work for us as we mainly shoot handheld.

Thanks in advance!
--
http://www.flickr.com/photos/subhrashis