For the 7950, you might be better off going with UBuntu 14.04 and using the fglrx 15.12 (they are in one of the Ubunty repositories with "-302" as part of the name) drivers.
I'm not sure if the "PRO" stuff supports older cards, though in theory it SHOULD work with anything GCN.
I actually went down that path too since making that post. I did away with the USB OS disk and found a regular disk. Tried a fresh UB 14.04 which was a fail, then tried UB 14.04 and installing the catalyst drivers failed. But I downloaded them instead of looking in the repo... I should try again with the repo versions I guess. Would using UB 14.04.5, would that have been a problem?
This was my error:
$cat /usr/share/ati/fglrx-install.log
NOTE: If your system has logged the missing packages required for installation, install them in the order as per the log file to resolve package-dependency issu
es.
Supported adapter detected.
Check if system has the tools required for installation.
Uninstalling any previously installed drivers.
Creating symlink /var/lib/dkms/fglrx/15.302/source ->
/usr/src/fglrx-15.302
DKMS: add completed.
Kernel preparation unnecessary for this kernel. Skipping...
Building module:
cleaning build area....
cd /var/lib/dkms/fglrx/15.302/build; sh make.sh --nohints --uname_r=4.4.0-78-generic --norootcheck.....(bad exit status: 1)
[Error] Kernel Module : Failed to build fglrx-15.302 with DKMS
[Error] Kernel Module : Removing fglrx-15.302 from DKMS
------------------------------
Deleting module version: 15.302
completely from the DKMS tree.
------------------------------
In the end I threw Win10 on it and it just worked... (Except that the second card went to full fan speed almost straight away, will look into that).
I guess I need to try UB 14.0.5 again and try installing from the repo...