Damn... I added 4MH to the pool just by installing new drivers (14.6 RC), new sph_sgminer_14.6 and small changes to the configuration

GPU 0: 60.0C 1324RPM | 3.949M/4.019Mh/s | A:14 R: 0.0% HW:0 WU:0.048/m I:20
GPU 1: 65.0C 1359RPM | 3.976M/4.025Mh/s | A:8 R: 0.0% HW:0 WU:0.047/m I:20
GPU 2: 59.0C 1355RPM | 3.952M/4.019Mh/s | A:21 R: 0.0% HW:0 WU:0.072/m I:20
Settings for these MSI R9 280X Gaming (undervolted: 956mV iso 1500mV):
"expiry" : "1",
"no-submit-stale" : true,
"queue" : "0",
"scan-time" : "1",
"auto-fan" : true,
"gpu-threads" : "2",
"vectors" : "1",
"gpu-dyninterval" : "7",
"gpu-engine" : "1000,1000,1000",
"gpu-fan" : "30-65",
"gpu-memclock" : "1500",
"gpu-powertune" : "20,20,20",
"intensity" : "20",
"kernel" : "x11mod",
"temp-target" : "75",
"temp-overheat" : "78",
"temp-cutoff" : "80",
"worksize" : "128",
"thread-concurrency" : "8192",
"no-pool-disable" : false,
"loopup-gap" : "2"