here are things you should look at.
clocks can vary infact it might be why you choose to flash. same with voltage they kind of go hand in hand with clocks. you need to be careful however and make sure your cooler can handle it. bios size memory amount and bus width cannot be different. that will result in a brick. Also things you may not see. different manufacturers may use different chips. different chips may have different latency's and timings. flash with too high of a clock speed and the chips may not be able to take it. rule of thumb. make sure your card can clock higher than the clocks of the bios you are going to flash. this reduces the risk of a failed flash. These things are all things to consider and all of these things are part of the risk in flashing. Be their no confusion Flashing is dangerous and risky. it is upto the owner to decide if it is worth it.