I was having the same problem on Friday. I bought two of these:
VisionTek
Radeon R9 290X 4GB GDDR5 PCI E
Manufacturer Part#   900654
UPC Code:   784090032133

I've had one of them running for 50 hours now at an average of 975Kh with this config
"intensity" : "20",
"vectors" : "1",
"worksize" : "256",
"kernel" : "scrypt",
"lookup-gap" : "2",
"thread-concurrency" : "28650",
"shaders" : "0",
"gpu-engine" : "1050",
"gpu-fan" : "50-100",
"auto-fan" : true,
"gpu-memclock" : "1500",
"gpu-memdiff" : "0",
"gpu-powertune" : "20",
"gpu-vddc" : "0.000",
"temp-cutoff" : "95",
"temp-overheat" : "85",
"temp-target" : "78",
"api-mcast-port" : "4028",
"api-port" : "4028",
"expiry" : "120",
"gpu-dyninterval" : "7",
"gpu-platform" : "0",
"gpu-threads" : "1",
"hotplug" : "5",
"log" : "5",
"no-pool-disable" : true,
"queue" : "1",
"scan-time" : "1",
"scrypt" : true,
"temp-hysteresis" : "3",
"shares" : "0",
"kernel-path" : "/usr/local/bin"


I was getting the "error -4" message in cgminer when I tried to run the higher TC (this pc only has 4gb of ram). So I worked out this config with one card and when I installed the second card, cgminer would go blank and never run. From there I tried several different configs and nothing worked. The only progress I made was when I installed the drivers from the catalyst 13.3. With that I was able to get cgminer to load, but all I could get was 100% hardware errors, even while testing a few different TCs.
 Hopefully tomorrow I'll have more time to work out the issues, and I'll test them in a different PC .