Nobody knows. With a very high quality psu, sure, you could get away with it if you didn't push the graphics very hard. With a poor excuse for a psu shaped object, you'll be lucky to get into windows.
Since there really are no very high 500w psus I can think of, just a ton of mediocre models, I'm inclined to believe in choice #2 and you have a hunk of junk psu.
So the Question isn't if it'll work for a month or two, it's just how much value you place on the @ $800+ worth of cpu/gpu/mobo you plan on. Because a hunk of junk will have bare minimum protections, if it really has any, and those protections can be set so high as to be worthless.