With a 530w 87% efficiency psu you could run two r7 250s but it could stress your psu but if your fine with that you should go for it. The upgrade will defiantly give you a performance increase (probably by about 50-% as the second gpu will be on a pci.e 2.0 slot). Just remember you need adequate cooling in your system so it doesn't get to hot in there but other than that you should go for it.