The only downside so far is that I have 2 out of 60 GPUs that persistently hard hang after anything from 5 minutes to 3-4 hours.
I have the same issue. I have five 7950 Club3D and four of them are playing nicely with g=2, xI=4, threads=8192 @670kh/s, however one of them just hangs after a couple of minutes so I have to use g=1, xI=300, threads=24000 @650kh/s