It is quite relevant as unfortunately this may be a Hardware issue.
I had an R5 years ago and it ran GTA SA fairly well but I wouldnt expect anything special, I'm surprised you can run GTA V if I'm honest but that's a good thing!
Try uninstalling your current GTA, also removing any traces in your APPData > Local > Rockstar Games > [Make sure you have hidden files as visible] and THEN updating your GPU drivers:
http://support.amd.com/en-us/download TEHN reinstall GTA sa after a restart, see if that does the trick.
My money is on a Hardware issue though.