it doesnt matter when you do the bios flash. if the settings doesnt work for you, mod them a bit.
after bios moding and flashing it back to the GPU , start with standard settings 1100 or 1150 core clock, insert 850 mv core voltage, and memory controller voltage 800, memory clock 2000.
after getting it work stable for 1 min, increase the memory to 2050 , wait a bit , check how it reflects the mhs. if its all stable increase to 2100, and check again, if it crashes, reduce to 2070.after finding stable stop, if you want you can increase core clock from 1150 to 1160, 1170, if it crashes you will need to add more voltage to the core so increase core voltage to 860. if it crashes increase a bit more.
its all about finding the sweet spot. which from card to card may vary.