safe voltage on 9600 GT

[cyberfish]

I have a Gigabyte 9600 GT (the version that comes with VF700-AlCu) that comes with Gigabyte's Gamer HUD which allows overclocking and changing voltage. Has anyone had experiences with this? How high can I safely take the voltage up to? from stock 1.1V. On "stock" cooling (VF700-AlCu).

Thanks

*edit* correction made. Should be VF700 not 900.