290x Lightning not overclocking well

[Stardust342]

I have a 290x Lightning waterblocked, and I am trying to do some overclocking. I started with a 100 mhz core clock boost, and that was easy enough. I added another 100 and it was still fine. Then I added just 50 more and it artifacts on Valley. I have power limit and all the voltages maxed out and BIOS in LN2 mode and it cannot run valley without getting instant artifacts.
Here is a screenshot of my settings

Mem is +100 and aux +50
I'm pretty sure I should be able to turn up the core clock voltage above +200mhz, but it won't let me. Here are the other settings I have set

Also, my Asic Quality is 76.4%
Did I just get really unlucky or is there something wrong with my overclock software? Any ideas? Thanks.

 

[Stardust342]

Ok, so I did some research and this is actually about average, but how can I unlock voltage past +200mhz? Would I have to modify vbios or is there a way I could do it through software?