As of one week ago, I have been running my R9 290 on stilt bios @ 1125mv (voltage). A few weeks ago, I reduced the mem clock from 1250 to 1125, as well. This resulted in an increase increas of hashrate by 1mhs per GPU, on average.
However, after latest DAG change, 25% of the GPUs crashed immediately. I am finding they require, on average 20-30mhz reduction in core clock to fix stability issues.
I have seen reports that moving 1125 mem clock back to 1250 mem clock fixed this problem, but at the expense of 1mhs.