That setx GPU_MAX_ALLOC_PERCENT 100 is not inside cgminer.conf, but a command at the cmd.exe prompt

Inside the config file, use:

"intensity" : "20",
"lookup-gap" : "2",
"thread-concurrency" : "24000"
"gpu-threads" : "1",

or

"intensity" : "13",
"lookup-gap" : "2",
"thread-concurrency" : "8192"
"gpu-threads" : "2"

alongside the remaining settings