I did a lot of research that suggested that the GTX 660Ti would work, however I bought one and there is a heat problem. Not so much a power issue, there seems to be enough head room on the 330W PSU, but the case is so small that if you are running any new games worth playing the GPU raises the temps inside the case to much. I installed an gadget to watch the temps and my CPU got up around 80C and shut the computer down. you can run a little better if you get the ASUS 660 with the integrated duel fans. I am taking a different route and am going to take all the components out of this little x51 case and transfer them over to a new case. That will solve the problem from the heat, and I can upgrade the power supply.