Coming back to share some settings, as promised, now that I've found something that seems to be working stable.  

Gigabyte R9-270 | win7 64, amd catalyst 14.4 | on x13mod hashing ~1.65mh/s per card

"intensity" : "18",
"kernel" : "x13mod",
"worksize" : "128",
"lookup-gap" : "2",
"gpu-threads" : "2",
"shaders" : "1280",
"gpu-engine" : "1110",
"gpu-memclock" : "1475",
"gpu-powertune" : "20"


Sapphire R9-280X | Xubuntu 12.04, amd catalyst 14.4 | on x13mod hashing ~2.65mh/s

"intensity" : "18",
"kernel" : "x13mod",
"worksize" : "128",
"lookup-gap" : "2",
"gpu-threads" : "2"
"shaders" : "2048",
"gpu-engine" : "1160",
"gpu-memclock" : "1500",
"gpu-powertune" : "20"

all you gotta do is add your pool/fan/temp details as normal and it should blast off.

Note that I have not thoroughly tested these for days on end yet. I'll report back if shit goes haywire and I need to reconfigure.