Upon further review..
Earlier this week I lamented about borrowing and using Williams' Sony 70-400 while out on a bird shoot. I found the lens great and I had a lot of nice photos in the short time I used it.
I went back and reviewed my photos that I shot with my Sigma 120-400 HSM OS. I have gotten good results in the past and I found a few keepers in this outing as well.
There are some definite advantages of the Sony such as focus limiter & focus hold buttons. Not to mention sharp wide open. But my cheapo Sigma held up OK, for now. I am keeping my eyes open for a super deal on the Sony if & when it comes available to me.
Had a great time checking out equipment and shooting birds.
I have to recommend to other forum members, if possible, meet up with other shooters in your area, and get out for a photo day. It is really a treat to "talk shop" with others who share our interests. I know I will be meeting up with William & George again this year if & when it ever warms up!