I know he isnt using sli or crossfire..... i had 2 7900gtx's.. i sold them and bought 2 x1900s. With no overclocking, i got over 1,000 points more in 3dmark06 with the xts. When using high resolutions like 1900x1200,, the crossfire stomps a hole in sli's butt. turning everything up, oblivion was super jerky, almost unplayable with the 7900s.. with the x1900s,, nice and smooth.
But still, he probably wont be playing on a big monitor or OCing.... so in that case, i would say it dont really matter. I heard that the 7900s OC better, but he wont be ocing. So going by the high end data, i would say to get an x1900.
Most people here cant really compare a 7900 and a 1900 because they have not used both.
single card on default settings in 3dmark06... the x1900 got about 600 points more