i've not heard of this before got anymore links or info?
Ok, what I think is happening is that the power delivery systems on these two cards (at least) is absolutely subpar, causing too much vdroop. The ROPs/IMC on Tahiti require higher voltage than the rest of the core, making this deficiency only show up on ROP intensive workloads.
The combination of a high actual core utilization of the chip plus the high utilization of the ROPs make the vdroop caused by the inferior power delivery system to cause a hardlock in the operating system.
This is exacerbated in the design of the XFX Double Dissipation Black Edition 1000 mhz especially since the VRMs are placed in such a way to have low actual airflow, leading to extremely high temperatures.
These high temperatures were tolerable in the reference board design, but the subsequent switch to XFX's custom board design lead to obvious deficiencies in many parts of the board.
This was obvious to these two board manufacturers, so they put something in their bios's that probably limits core speed drastically when they detect compute heavy workloads.
This explains the severe under-performing in Litecoin workloads at stock speeds.
When you force the cards to stay at the supposed "stock" speeds with MSI afterburner, they will work for a while until they hardlock the system.
This even carries onto lower clock speeds.
This is evident since the Litecoin workload actually does NOT bump into the powertune limits, because it does not fully utilize the compute section of the card. The extreme stress to the ROP/IMC section of the card is what causes the hardlock when combined with the vdroop from both inferior power delivery as well as the inferior cooling provided to the inferior power delivery.
The crappiness of these two cards for Litecoin workloads is common knowledge throughout the litecoin community.