I found a Mac Pro 1,1 a while back as someone threw it out. I tried turning it on but there was lines all over the screen. I tried booting OSX, Linux and Windows but all of them kept crashing and caused the system to reboot.
I did what Linus did a while back and put the stock graphics card (GeForce 7300GT) into my oven for a while and it started working again (despite 2 capacitors blowing up in the process). Since then I've been excited about attempting to game on this thing but I cannot due to the crappy GPU that's currently in it. I'm not someone who can just afford to go out and buy another graphics card but I've always wanted to play PC games instead of playing titles on my laptops iGPU (HD 4400).
The Mac has PCI-Express and I've seen videos on the internet of people gaming on it with a GTX 980. I've never owned a proper a graphics card before so finally having one would be such a dream and it would be so exciting to be able to game on this old Mac Pro. A budget gaming rig is what I want and this graphics card would surely put new life into it.
I don't use OSX and this Mac is practically a PC now, I only use Windows and Ubuntu so this GPU should be perfect and the only thing I would be missing out on is not being able to see the EFI screen (which is completely useless anyway IMO. Apple love making things "simple").
Any graphics card is surely to be better than the old 7300GT, which still has a few graphical glitches of its own.