I think it's the 5000's and up that lost support with 16.04.
I believe that is correct. I am told by 14.04 that no proprietary drivers are available with the Radeon HD 4650 currently installed in my system. The 4650 meets my current needs as is, but I do like to do upgrades occasionally. I will probably install a Radeon HD 7750 by the end of the year. Time will tell if there will be a proprietary driver available. From what I have read I think (hope) the open source driver in both 14.04 and 16.04 will support the 7750. That should really be enough for me, in any event. I am held back in the graphics card arena by the need to maintain hardware compatibility with the Windows XP side of my dual boot system. It must be an enormous task for software developers to keep track of hardware variations and determine what they can continue to support with any software release. What a challenge! I think they do a commendable job.

Regards