Yeah, your gpu-engine is really low. Should be able to push it above 1100 quite easily. Also, I don't really notice much difference at 1250 memclock versus 1500. Settings between 1250 and 1500 will reduce the hash rate. It's got something to do with the memory latency profiles at each frequency. This will also vary depending on whether you have Hynix or Elpida RAM.

EDIT: crossed out section only applies to normal scrypt or X11 mining.