Is your 7950 Powercolor ?
Mine is and same with the intensity - 12 is max, if I go more the cards get very hot.
I'm using this
"gpu-memclock" : "1500",
"gpu-engine" : "1010",
"gpu-powertune" : "20",
both cards are sapphire, increasing the memory + or - by even 5mhz results in lower kh/s with the 7950, similar problem with the 7970, intensity 13 is the sweet spot with the settings im running at the moment.