I finally able to workaround those cards by RBE.
To successfully modified vcore and clock on bios you need to:
1) Save the bios to a file using GPU-Z
2) Open the file with the last version of RBE.
3) On "clock settings", go to "GPU Registers"
3) On "0x46" goes the vcore you want, i use "1.2100"
4) On "Clock Info 00", you can put the GPU/RAM frecuencys of you choice im using 950/350 for best results in my case. DONT change the voltaje setting... leave it at 1.088
5) Save and flash the bios.
I cant do anything about fan control, it does not accept any change by RBE, fan target seems to keep the card at 77°C.
Ive upload an already modified bios of a Sapphire HD5850 xtreme:
I recomend to keep an eye on VRM temperatures. they seems to go up like hell, ive installed an extra fan to help keep them cooled.