That's exactly what I'm talking about for testing.

As an example I am testing SMN pets at 751 SPD over 28 minutes VS base SPD of 354.

Pretty much. Even if it wasn't the case If you needed 300+ SS to see one more turret auto in 3 minutes it would not even be worth it.
Not exactly looking whether it's worth it or not, just whether it is effected.

Thanks for checking though, and if you could do a comparison of high SPD over 20 mins or so VS base SPD. that would be awesome.