Switching manufacturers will either brick your card if it's a non-reference design or make no change if it is a reference design (since all manufactures use the same VBIOS on reference designs). The only BIOS flash that could help would be one of the ones that "The Stilt" created. They have optimized memory timings that could make a difference. Open GPU-Z, find your card's BIOS version and memory manufacturer, then search this page to see if there's a modified version of that same BIOS and memory manufacturer. I came across that repository yesterday. I thought all the BIOS files were lost since the original links on the original forum post were dead. I'm going to try one on my Elpida powered Powercolor 7970 that will not get over 550kH/s no matter what I do to it, and I'll report my results.