Hello i would just like to know what the Asus M5A78L-M LX would support ? . i currently have a gtx 660 installed on it and a FX 6300 on it. in 1-2 years i would like to get a 770 or a 780ti (if possible the 8*** series of Nvidia range) could i do this with the motherboard?? or is it restricted to this or lower cards? . i have a 500Watt psu by the way . would i have to upgrade? (8gb of ram i also have)
If you can run the GTX660 with no problems, you will also run the GTX 7xx series, just be sure that you have a very good PSU (Seasonic or the like), with at least 40 Amps/400W for +12V rail (GTX780Ti has max. 300W power draw), and that's if you don't overclock anything.
Just bear in mind that PSUs degrades their quality over time, so in 1-2 years you will change the PSU anyway.
Also, for your FX6300 a GTX770 will do, as anything above that will be overkill; you will see benefits going from 770 to 780/780Ti or R9-290/290X only if you will change the platform (at least an i5 or an FX8xxx).