Do you still have the 150-500? If so, would you be able to take a pic at 500mm on the Sigma and 600mm on the Tamron on a subject approx 30 metres away? Also, is the AF on one better than the other? Cheers.
I do still have it. Here are a couple shots two days ago that are pretty close to your request. They were taken at 60 feet, or about 20 meters. Both 100% crops, nothing done to them.
Tamron | 600mm | 1/320 | f/9
Sigma | 500mm | 1/500 | f/9