I can understand that you are getting tired of console gaming, a lot of people are, in fact, console gaming is said to be dead within the next 5 years. Im sorry to say, but i do not think you will get a very good build for that budget. You need to get a motherboard, CPU, RAM, HDD, Case, GPU, PSU. People can just barely get away with a good build for 800. If you goto a site such as e-bay, your chances are a lot higher as second hand products are cheaper, however there is the risk of them being faulty. People like to sell products that are faulty with out telling the buyer. So i recommend you save a little more, preferably around 800-900. You maybe could sell your console and get an extra 240-300. And for SLI & Xfire (crossfire), are the same thing. But, SLI is Nvidia, Xfire is ATi. It is just running two graphics cards together for better performance. To understand how this works, A graphics card (GPU) must process frames per second (FPS), in general you want atleast 20 fps or more or it will be choppy like a slide show. GPU has to process 20 FPS, every second, which puts stress on the GPU, Having two allows one GPU to process one frame while the other gets one ready to process after the first. So they have that split second intervill of extra time to process, which give better performance, however it requires more power and generates more heat. And not all games support this. Sorry for the long answer. I hope this helps.