I'm sure its possible I have seen some people get OCs far and beyond what I would expect them. I have 3 65 NM 9800GTX cards. But they can only reach about 730 Mhz core and 1800 on the shaders. I'm sure there are some impressively binned 55 NM 9800GTX out there just as there are some 65 NM 9800GTX cards.
Nice overclock btw.