certainly would change things up, though some folks using 160mm anyway.
Though if you "generalize" and for sake of argument you estimate each inch of travel to be approx a deg of head angle change, the 2006 RC2X (I assume you have the 170mm version), the head angle would change from from the posted I think 68.5 deg head angle at 518mm fork (which I assume means static/unsagged measurement) to then about 67 deg [68.5 - (555mm AC - 518mm AC) / 25.4 ]
However, if you then estimate using this estimated 67 deg static head angle that you will run the 170mm fork using about 25% sag, that would put you in a "riding" head angle of about 68.7 deg which doesnt sound bad to me for such a bike
Though if you "generalize" and for sake of argument you estimate each inch of travel to be approx a deg of head angle change, the 2006 RC2X (I assume you have the 170mm version), the head angle would change from from the posted I think 68.5 deg head angle at 518mm fork (which I assume means static/unsagged measurement) to then about 67 deg [68.5 - (555mm AC - 518mm AC) / 25.4 ]
However, if you then estimate using this estimated 67 deg static head angle that you will run the 170mm fork using about 25% sag, that would put you in a "riding" head angle of about 68.7 deg which doesnt sound bad to me for such a bike