It's pure speculation to guess what the power requirements will be for a future series of cards especially considering that the GTX660/660ti haven't even been released. What can be said is that GPU power requirements have consistently decreased with this generation of GPUs. If power requirements don't significantly increase in the next generation of GPUs, then a good quality 500W PSU will likely be sufficient. This is pure speculation, but in today's 600/7000 series GPUs a good quality 500-550W PSU is sufficient for any single-GPU card. What is the make/model of your current PSU?