While this will work it will run very very very slow because the 4 chars are static. To make any reasonable use of GPU you need to give it some work to run on GPU kernel.
So you better get oclHashcat-plus v0.09 and use the sha256(salt.pass) hash-mode and -a 3 attack-mode and see speed increase by 100-1000
So you better get oclHashcat-plus v0.09 and use the sha256(salt.pass) hash-mode and -a 3 attack-mode and see speed increase by 100-1000