for 1280x1024, even a 4850 is an overkill, never mind the 5xxx series then...so i suggest you to answer these questions below..
are you gaming? if so....is 1280x1024 your gaming resolution ?
are you going for max settings in games with AA and AF?
Hey,can you edit your post in this format, as it answers a lot of questions that we may have, then we could give you the most suitable answer:http://www.tomshardware.com/forum/261222-31-build-advice