I was having a lot of trouble getting El Capitan to work with my 5450, mainly because I couldn't modify the kexts or install any with kext utility, kept getting errors. Finally after a fresh install, I tried just adding ati5000injector(modified to look for amd) and i was able to get the graphics card to work. Before I modified El Capitan to boot up with my mac pro I had turned on screen sharing so I could see if it was working and make changes for the card. Now that its working, I'm having all those issues of sluggishness and refresh and reboots. I had this problem before with Mavericks I believe, but can't remember how I fixed it. It might have been by removing or adding ati accelerator, but I'm not sure. Has anyone had this problem that they were able to fix? I've already tried searching, but there's so many posts and none seem to have the answer, only to install the other kexts which don't work.