I think the only way to go past the 840 MHz limit (besides flashing a 6970 bios) is flashing the Asus bios, according to Techpowerup.

Maybe a future version of the Radeon Bios Editor will allow editing the overdrive limit, so we can just modify our card's bios, just like with the shader unlock. That'd be the best option, imo.

@racerx: Slush added a two hour delay for any blocks found by the pool in order to avoid cheating by malicious users. Give it a few hours and you should see some rewards in the 'My Account' section in the pool's site. When the confirmed reward is over the threshold you set, it should be sent to you.