Does not look like this has been posted yet, and sorry if it has. Here is the link to MotorTrend's first test, article published yesterday...
https://www.motortrend.com/news/2020...00-first-test/
Here is the link to their test of the M6ZLE From June, 2017
https://www.motortrend.com/cars/chev...t-test-review/
Here is the link to their test of the base A10 ZL1 from December, 2016...
https://www.motortrend.com/cars/chev...e-squad-goals/
I could not find an auto ZLE, or M6 ZL1, but I did not look that hard. Maybe someone else can find and post those.
Overall the ZL1 hangs with both trims of the GT500 really well. Unless you're a die-hard Ford/Shelby fanboy, or someone who needs to have the "latest and greatest" I think after reviewing all of these tests it would be hard to justify the GT500 over the ZL1.