Had some problems at the start, the display got black and the computer froze when I used applications that started to tax the card. After a PRAm-reset that problem disappeared.
However, as I have written in some posts at the end of this thread, https://forums.macrumors.com/posts/18000837/
I measured a somewhat bothering power draw from the "converted 8 to 6-pin power cable". It drew about 70% more power (max at 128W) than the connectors on the motherboard are meant for (75W). It may, or may not, be a problem in the long run. I very seldom use the cards max capabilities, otherwise I would have been more concerned. Even if the card is clocked down, the 8-pin connector draws much more than 75 W during load.
Other than that the card works very nicely. I bought it mostly since its connectors match my needs (Simultaneous DVI, Displayport and HDMI) and it seemed like a good idea to have a bit more reserve compared to the 7950, for the future.