Flashing bios to increase performance potential

Hi all, I recently flashed my gpu bios in an attempt to enhance my Powercolor Radeon 5850 pcs to a 5870 OC potential. I think I did it correctly because the bios version on gpu z now displays a revision number.
I downloaded and used Radeon bios editor and Ati winflash to edit the file.

I have always overclocked the card from stock 760/1050 to 800/1050. It will run stable in furmark and heaven.
After editing the bios I’m still not able to OC the gpu any higher. I’ve read people are running this card up to 925/1150.
Am I doing something wrong?

Would heat sinks on the memory chips in the gpu help? I notice more current gpus have thermal protection of some type.
Is it advisable or should i have re installed the drivers after editing the bios?

Thanks for your time.
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