Light where I live in the North prohibits high shutter speeds much of the year. I normally shoot Tav and offhand and it was only a week ago that I started seeing iso 100 flashing, and normally use 1/400 shutter and 6.3 or 7.1 and usually end up with high ISO but am very pleased with with the DA 1.4 and DA* 300. In the last 2 weeks I am able to push shutter speed but usually choose Aperture to increase DOF. Because the DOF is so shallow sometimes I think people confuse it with pictures being out of focus.
f/11 at 1/400 which caused ISO to jump to 5000
f/11 at 1/400 with a bit more light allowing ISO at 1600
The tc really helps focus in where branches would have not allowed the DA* 300 by itself
And a very wet eagle...
This is half way across the Mississippi river. Granted it is the upper Miss but still quite a distance away
Those pictures are all handheld. For tripod mount, DA* 300
With DA 1.4x tc on tripod
I can't drag a tripod into many of the places I go. And don't see much of a disadvantage to it, most of the birds I shoot don't like to sit still and pose for me anyhow.