Previously I rented the Sigma 150-600mm 5-6.3 Sports DG OS HSM Lens for Canon. With both lenses I was using the Sigma MC-11 Canon to E-mount adapter to shoot them on my Sony A7 III. My impression of this lens is positive. It has good sharpness even at 600mm and autofocused well on the MC-11, Sony A7 III combination. Comparing this lens to the Sport version I would say that you are looking at a number of trade-offs. I’ll start off by saying that both of these lenses are good. Both have good image and build quality.
But the Contemporary lens is half the price ($990 vs. $1,800) and 2 pounds lighter (4 ¼ lbs vs 6 ¼ lbs).
On the flip side the Sports lens is a solid metal lens and has superior image quality.
Comparing their image quality, I would say the Sports lens has decidedly better contrast that holds up better at high light levels. So, there you have it. If either a 6 ¼ lb weight or an $1,800 price tag is too much for you then you will get a good lens for your $990. But for the best image quality you’ll have to go for the Sports lens.