The X1950XT is in another league, the 7800GS cannot even touch it, the 7800GS is just as fast as the X850XT PE in most scenarios, sometimes slighly faster, sometimes slighly slower. The X1950XT is the fastest AGP card on the market, then is followed by the 7950GT and then by the X1950PRO, X1950GT and 7900GS. But the X1950XT cannot be found that easily, neither the 7950GT, if you can find it great, otherwise the X1950PRO or X1950GT can fit the bill nicely.
And the differences in current and future games will simply make the X19XX Architecture to wide it's advantage against the G7X architecture.