Dependso n your Temps, how are your VDDCs holding up? Looks liek 1.2-1.25 is pretty normal although
these guys are saying 1.34v for near 1000 MHz
As long as VDDC temps are good (along with the obvious core temps) I dont think I would go much past 1.3 on stock cooling.
(I almost kept a straight face the whole time I typed that

) I was pushing 1.45 on the 4890 with the stock cooler, would push it higher, but I think that is the max that the card can actually push. Saw no benefit running 1.46+