Some systems experience this behavior. Just yesterday, I tested the same 270 card in 3 different systems (Conroe based, Toledo based and Haswell based). And only Haswell based system could reliably recover from sleep. Other systems had various "black screen" issues (with the fans spinning
and not). The failure rate was not 100% though, sometimes it worked ok. I did about 20 runs. Go figure, what kind of incompatibility this is. Moral of the story, if you are not sure, go with nVIDIA. Alternatively, you can disable ZeroCore tech by preventing your monitor to go to sleep. See attached picture.
But when it works, it
is great. My 270 Crossfire Haswell rig pulls just slightly over 30 watts (1HDD + 1SSD) from the outlet, during the night.
Just a few watts over what HD 4600 would do in this scenario. Kudos to AMD.