Hi Steve,
Thank you, how did you remember me? It's been a few months since my last photo...
Re: the sharpening and framing: see
Absolute Sharpening Pro. And, it makes a difference when you shoot in RAW.
I have no experience with the Sigma, sorry. But the quality of my FA* 80-200 is such that I will never sell it. It has the perfect combination of bokeh and sharpness, in such a way that even 100% crops are super sharp and pleasing to the eye. This is a Dutch topic but it explains it well (many of the photos were big crops, please click on them to see them in the right size):
(Na)bij de Kikkerpoel
Some more with the FA* 80-200 (again, click on them):
Eendenkuikens in het slijk
The Sigma could be in the same ballpark, but I honestly do not know.