POST DISCLAIMER: I've had no problem with this system sleeping a 7870 and 7850 CrossfireX setup and later coming back to game and would appreciate some thoughts from others on this.
Since upgrading to a single GPU (RX 480) trying to game consistently, after sleeping my system and returning later, results in tearing/games crashing and both HWiNFO64 v5.50 and v5.52 report GPU Memory Errors. Additionally post returning from sleep I have once, thus far, seen my desktop being a lovely snow show straight out of Poltergeist that goes away with power cycling the display but I've found I am not alone in that and such is a driver problem that eventually should get fixed.
I can't say it is the card as I can, from a cold boot or reboot, go hours without any tearing/GPU Memory Errors while looping any Unigine benchmark or playing any game. FYI the Prolimatech MK-26 and two Ultra Sleek Vortex 14's keep this card below 56C (132.8F) in 22C (71.6F) weather so I doubt this is a temperature issue. The max temp I have reached on any day with this card was 65C.
ATM I am using the WHQL 17.4.4 driver. Prior to installing such I DDU'd my AMD driver installation before taking out the before mentioned 7870/7850 CrossfireX cards.
Please toss out ideas. My complete system specs are as follows:
Corsair TX850W (CMPSU-850TX)
Gigabyte 990FXA-UD3 (F9 BIOS) w/HT Link at 2500 MHz and NB at 3000 MHz
AMD Phenom II X6 1090T at 4125 MHz (w/Noctua NH-D15)
16GB Mushkin Enhanced Redline (991981) at 1666 MHz 10-10-10-24-33 2T
Sapphire Nitro RX 480 OC at 1400 MHz/2000 MHz (w/Prolimatech MK-26 and two Ultra Sleek Vortex 14's)
Creative Sound Blaster Z
OCZ Vector 180 480GB
WD VelociRaptor WD3000HLFS 300GB (10K RPM)
Windows 7 Ultimate X64 Service Pack 1 Build 7601