Brighta :
If i changed the fx 8320 to a fx 6300 could i run it all on a decent 500w psu?
230W for the GTX770 no matter what
50W for mobo/HDD/etc (estimate)
95W for 6300 versus 125W for 8320, not a huge difference
230+50+125 is 405W, plus 20% due to inefficiency is 485W
230+50+95 is 375W, plus 20% puts you at 450W
As you can see, not a real benefit / savings. If you have a 500W Platinum then you might be just fine, but really for the same or better price, a 550W Gold or 600W Bronze would be safer.
If you have any remote thoughts of overclocking, add another 10% to 20% to the above.
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Edit: to clarify. That 20% extra for inefficiency is the PSU inefficiency. An 80 Bronze needs that 20% buffer so those results are really pushing it if you do use a 500W Bronze. Could run fine for a bit, but I'd anticipate shutdowns when you run games hard on the 8320 chip.