The 2GB "reference" 6850 (i.e. turbine cooler and sealed card case) are hard to find now but easily flashed to 6870 (unlocks the full 1536 shaders). I then overclock them to 940 / 250 ( @ 1.175 VDC). I can get them to 950 but I usually get a crash once a day and if they don't restart the lost time isn't worth the last 10 Mhz.
As far as I can tell, AMD never officially sold a 2GB version of either the 6850 or 6870. Ok so there's a 6850M that comes with 2GB RAM but that's based on the Juniper design, not Barts.
Also the 6870 GPU only has 1120 SPs so to get 420 Mh/s you would have to supercool your "6870" and run it at ~1300 MHz.
By this point, I think your 8 key is too close to your 9 key. 420 Mh/s isn't unreasonable on a 6970 or unlocked 6950.
I'd go so far as to say the keys are mislabeled on his keyboard... that'd be 10+ typos lol
But yeah, surely he's referring to an unlocked 6950...