I just got 6 xfx 290 cards, apparently the xfx/powercooler had the best chance of unlocking. These are a later sku number though, so I've got no faith at all in success. I've also heard of plenty 290's "unlocking" but the shader count stays the same. I hardly call a higher stock clock "unlocked!"
Ya I'm looking to flash the 290x BIOS for 2 reasons: 1) see if I can get the full 2816 cores, and 2) get full voltage control. I've read reports on both happening on these Powercolors, which seem to react pretty positively to the flashing, but we'll see.