MC7's and pro300 DGs aren't legacy models. They're still being sold.
There was a german test that showed the MC4s were the sharpest. They have been tested, and they DO introduce more flaring. I know for a fact, because I own 1.4x and 2x MC4s, and I used to own the pro300s.
I would contend sharpness is the most important factor with a TC. There is so much degradation to sharpness when you slap one of those babies on anything but a giant super telephoto.




\
