Yes 1.3v is perfectly fine if not a bit more than what 4ghz would need to be stable, just keep an eye on temps, I generally recommend to not go much above 62C on the cores, the socket temp will sometimes vary between motherboards in my experience and is not really reliable.
Now temps below 40C on pretty much every FX and Phenom is a wash, its not accurate, its how AMD gets their readings, some FX chips will idle at or below room temp which isn't possible for a 95 or 125tdp chip, anything above 40c is accurate according to AMD's data.
FX the safe maximum voltage everyone recommends is 1.55v, although you would need some vary good cooling, and thats 5ghz territory, a lot of even higher end boards don't handle that kind of voltage and power draw well.
I was able to get to 4.4ghz on stock voltage on my 8320, I hit a wall around 4.7ghz and was able to get to 5ghz at 1.53v and was able to get a stable 5.1ghz at 1.56v although it was starting to over whelm my water cooler, and that was on a decent 12+2 phase motherboard, If you still want to push that FX more, just make sure your motherboard is up to the task, Many boards out there that say they can handle the FX 8 cores but can only really do so at stock and nothing more. And every chip clocks differently.
I still have my FX8320 I bought in 2012, hardly used anymore these days, but I keep it just because it was a fun platform and Idk, I just don't want to part with it yet lol.
thx and i set the cpu ratio x20 and the bus clock 205 i change the voltage because in prime95 he say 1 error 0 warning so i up this to 1.340 (i was on 1.32) and now 0 error 0 warning i think it good but hey thx guy