I don't think all of the FX 5700 Ultras have that GDDR3 memory. I just saw a review that was writtin in march about it's design, but I don't know if it became standard or what.
But a flashing of the BIOS doesn't simply turn a card from plain into Ultra. That requires modding it and then flashing the BIOS so it gets recognized as an ultra. I don't believe such mod exists for the 5700.
The closest mod to that is the 6800, yes it doesn't have GDDR3 memory, but you can still mod it to Ultra speeds, but of course it wouldn't technically perform quite as well.