I would say a GTX 770 and you will consume about 350 watts in total. But here is a side note, you don't want to run your power supply 90-100% of its rated wattage 24/7. This is to prolong the life of your power supply. If you want to run a GTX 780 Ti (your cpu is more than capable of), you need a 650W so it will not run at 90%. More info is this video. https://www.youtube.com/watch?v=ajiN9aVOv4A