To anyone who is not stable / crashes: Your card is running too fast and it crashes because you overclocked too much for your card to handle. Lower your gpu-engine and/or gpu-memclock. I have multiple 7950's and 7970's running X11 (previously) and now X13. 100% stable been running for days. Start with 1030 for core and 1400 for memory and work your way up little by little until you find the optimal speeds. This is not a "one size fits all". You actually need to put some work into it if you want optimal speeds.
How certain are you about this being the sole factor? I ran for months on Scrypt with my four 290X's at settings tailored for each one. Switched to X11 and was able to stay at the same speeds. But now going with Lasybears, like other 290/290X users I'm having a continuous struggle with sick GPU's. I've played with engine/memory settings, lowered the temperature settings, reduced intensity (and tried lower xintensity) and so forth, to no avail. It's getting frustrating. Oddly, only the 3 Sapphire 290X's are getting sick. I've never seen the stock reference 290X I have go sick while on this miner.
When the GPU goes sick it cuts the memory speed to 150 Mhz (i.e. about 10% normal), and manually trying to change it doesn't work, only rebooting does. And sometimes I get blue-screens instead. The X11 enhancement of this miner is critical to keeping me involved in mining and leasing my rig, but at the moment I'm dead in the water. Can't really lease my rig out under these conditions unless I badly derate it. The funny thing is that everything seemed to go south a week or so after using this miner, at a time not associated with any identifiable change point. If it was just one GPU I'd chalk it up to a marginal component getting flaky, but with three taking turns going bad, that doesn't seem as likely.
My current GPU settings for Engine/Memory (etc) are as follows. Can anyone with a 290 or 290X report settings they find to be stable?
"intensity" : "18",
"worksize" : "128",
"lookup-gap" : "2",
"thread-concurrency" : "25600",
"gpu-powertune" : "20",
"temp-cutoff" : "95",
"temp-overheat" : "85",
"temp-target" : "80",
"gpu-engine" : "1050,1040,1000,1010",
"gpu-memclock" : "1500,1498,1500,1500",
"auto-fan" : true,
"auto-gpu" : true,
"api-port" : "4028",
"expiry" : "1",
"failover-only" : true,
"gpu-threads" : "1",
"gpu-dyninterval" : "7",
"log" : "5",
"queue" : "1",
"scan-time" : "1",
"temp-hysteresis" : "3",
"kernel" : "x11mod"