if you are doing it in manual set it to what you want and test the changes. if it passes you MIGHT be able to use it. I still suggest putting the card under a load for a while after an OC to make sure its 100% stable. im not to sure what the max you can get on that card. you can also use the detect optimal frequencies. run it about 6 times or so and then get an average and try running that.
If you select 'manual overclocking', you get a warning that you have to agree to and then you are able to change the 'settings' option on that same tab.