OCing GPUs are like a lucky packet. Sometimes it may just not OC as much. ANY HD7970 will reach 1000+MHZ though. Which is VERY good. You have the fastest single affordable GPU on the planet... So be happy and enjoy.
HOWEVER your PSU is not the most stable, it could improve an OC with a more stable PSU. But doubtful, if you want to try, get a unit that will aloow Xfire so that you don't end up wasting to much cash for just a possibly better OC.
thanks a lot dude, im planning on getting a new psu anyways , so il try and see what happens ,and your right it is a great gpu anyway wether it oc's beyond 1075 or not