OC'ing a non-reference 5870

Righto folks

I have a Gigabyte non-reference 5870 which is this model :

http://www.newegg.com/Product/Product.aspx?Item=N82E16814125316&cm_re=gigabyte_5870-_-14-125-316-_-Product

http://www.gigabyte.com.tw/FileList/Image/vga_productimage_gv-r587ud-1gd_big.jpg

I can't seem to adjust the voltage as this is a non-reference design. I was able to reach 940-950 Mhz core clock stable with MSI Afterburner though. I also checked that many people use the Asus ATI Flash, but this will not apply to my card as it's once again, non reference.

I was reading on radeon bios editor and wondered if this will help me by softmodding my volt. I haven't tried it yet so I'm asking here if anyone has experienced OC'ing a non-reference 5870.

My aim is to reach 1000 Mhz core clock stable.