Okay. I wanted to post a few images to show what I was experiencing.
Here are two series of four images each. Pictures were taken with 50D using a monopod. All were shot in jpg format and have NO post processing done. I know this is not a scientific experiment and that the Sigma group is over exposed and a little further away. Also I realize none of these are really very good but I really wanted to post these sets to illustrate an example of what I was seeing with the focusing.
The first set was with the Sigma 100-300 f/4
Exposure 1/1000 sec
Focal length 250
The second set was with the Canon 70-200mm f/2.8 with 1.4x converter
Exposure 1/1250 sec
Focal length 217
1-4 with the Sigma 100-300
5-8 with the Canon 70-200 w/1.4x
Perhaps the biggest difference is that I am more familar and comfortable with my own Canon lens and need more time to learn the Sigma.
Hopefully, I could improve with this lens but it goes back to Lensrentals.com in a few days. Based on my two short experiments, if I had to buy one of the two lenses today I would probably choose the Canon 100-400 over the Sigma 100-300 f/4.