Max clocks appear to be obtained with cpu voltage to factory spec so it yields a bit less voltage than entered.
For true stability try 1.475 cpu, 1.475 qpi, a 250mv bump in the pll from minimum of 1.81 i believe to about 1.85 on the pll. Make sure the qpi clock is 6400 and the uncore i believe is half that but one setting higher is stable mean 3200 is ideal but i believe the next jump up works too and yields about 5gb's faster memory performance.
SInce the 980x doesn't need a 7200mhz qpi you might be able to run less on the qpi but 1.475 seems very nice regardless in terms of pure power output, stability, and temps.
Set ram to 1.55v if running at it's base just set ram to it's spec of whatever you have ddr3-1600 @ 1600mhz.
Northbridge can handle a 250mv hop from the minimum. Leave southbridge at minimum.
Should be stable at peak overclocks with the above settings.
Dell Precision T7500 : Dual Xeon X5675 @ 3.536Ghz X 24 Threads : 48 Gigabytes : Cinebench R15 : 1505 : AMD R9 390X 8GB @ 1173Mhz 1350mv 57599 Power Limit @ 1250Mhz memory error free on tight timings / since 1500mhz+ had errors galore