sorry for the delayed response, this is how I found it, hope this helps, srry for the long post.
Having seen what the Voltage table looks like on a 7950 I had a pretty good idea of what to look for on my 7970 ghz, that said I took the only default clocks I knew of, GPU core 1050 and GPU Memory 1500 and converted the numbers from decimal into Hex using an online converter like
remember to add 2 zeros to the end of your clocks, i.e. 850 = 85000 then converted into hex = 14c08 but notice that is only 5 digits long so you have to add a zero to the front of it = 01 4c 08, then you have to reverse the order so that gives you 08 4c 01, this is what you need to search for in your bios. what makes it interesting is just searching the bios for for a hex quadword likely will not find any results (at least it didn't in my case) this is because you only have 3 out of the 4 words that make up a hex quadword, so you have to search the bios for just a hex word example "08", and then another search for "4c", then another search for "01". I used a hex editor called FlexHEX and it has an option to "find all", this finds every occurrence of that value and highlights it, once they all highlighted scroll through page by page looking for three highlighted values highlighted next to each other, you'll know when you've found it when you've found your core and one or two spaces to the right you see the hex value that = your memory clock and then a couple lines below you'll see you memory clock hex value listed again only with a different core value listed to the left..
on my card POS (XFX 7970 ghz) it has three power states, top one is 3D gaming/high performance with core at 1050 & mem at 1500, then it has 2D at 500 core & 1500 memory and then the last power state is the 3D low performance/UVD which uses 1000 core & 1500 memory.
where my card uses the same memory speed for all three power states it was very easy to recodnise.