How much voltage you set it?
Because at 6mv 50% still cannot get it stable above 1100 core
1075 Mhz / +50% power target / -12mv (I undervolt the card)
1085 Mhz / +50% Power target / 0mv
1100 Mhz / +50% Power target/ + 6mv
1110 Mhz / +50% power target / +18mv
1120 Mhz / +50% power target / +24 mv
1130 Mhz / +50% power target / +36 mv
1140 Mhz / + 50% power target / +48 mv
Not tired to go any further then that. On occasions I do game on this machine I use 1075 Mhz Which MSI afterburner keeps defaulting to when the PC turns on or 1100 Mhz with the notch up in voltage. Seems stable in benchmarks and games I play bar the 1130 and 1140 result however.
I tried setting it at plus 6 or 12 save, then whenever I close afterburner and reset my PC it remembers all my settings apart from the voltage.
Do you think the water block is what allowed you to push it further? Did you order it through OCUK?
I did get something similar. Try setting up the profile again, delete and re save to profile 1 to see if it helps.
I think the waterblock played a part because prior to putting it under the block I would usually top out at around 1085 in benchmarks while 1150 was the daily gaming profile. But it may also be I am trying to see how much I can squeeze the card. Also each card differs, my first Nano did not get quiet as good over clocks as my current one does.
FYI, only water block it if you plan to go down the WC route anyway, the extra few MHZ under the block is not worth it from a price / performance perspective. The block does not seem to be for sale on OC website and I got mine from EK direct. I can't link to competitors, but a quick Google search for EK R9 Nano water block should point you in the right direction.