PCI SERR with AMD but not NVIDIA

[ecos]

Quick update: I managed to get a stable system with a lower PowerTune value (-8, works with 6990 and 290X), with some 5-7% performance loss, always keeping an eye on the total power draw reported by the PSU. Although no MB was evidently burned, once one becomes unstable, it remains unstable and only works with said power setting. Once a GPU stays in the "unstable" configuration for a longer time, it will never become stable again, even with a lower PowerTune value, it goes into the trash bin. Switching all customer units to NVIDIA over the next few months ... sad.

Many thanks for the feedback on this topic.