when buying gpu and you are concerned about compatibility, remember that if your board is pci-e, then the gpu must also be pci-e, agp for agp (old tech)
another thing that you should be aware of is your psu esp if you are buying a powerful gpu. make sure you have good psu as well. then of course the size if you have a not-so-large case.
i know you did not ask for all of those, i just thought it should help you out in the long run. also, avoid those ddr3 variants, they are slow