I am looking to upgrade my current gpu a 6670 to a 7770. I am also looking into othe gpus such as the 7870 and 7970 but they need an upgraded psu which I am willing to do, is the upgrade worth changing a psu for it or shall I stick with the 7770 since the psu won't need to be upgraded. And also what is the max size gpu that can fit in the xps 8300? Thanks for the help in advance. Luke.