All X800 and X850 series support SM2.0b
Well, there IS a significant difference between SM 2.0 and SM 3.0, but the X800GTO2 isn't SM 2.0; it's SM 2.0 extended, also called 2.0b. It also brings many new features to the table that SM 3.0 does, such as dynamic flow and loop control, more shader instructions processed in a single pass, and multiple rendering targets for quadruple+ the speed in performing lighting.
It still falls short of SM 3.0, though but not by much. How big a gap it is, and whether it matters at all, remains to be seen, as no one has been too keen to compare the two right off.