That would be a waste of money... specially on the long run. It wastes too much electricity and you'll never be able to fully double the performance of the GPU's. Its always a better option to get a recent and affordable GPU. Investing your money in SLI or Crossfire is far from being a perfect solution when you want things cheap and up to today's standards. Cuz if you do that, your electricity bills will hurt like hell while extracting very little juice from the cards true power... Not to mention all the problems with the noise, temperature, and even bad optimization in synchronized work output.