GOT IT:
http://forums.gamewinners.com/forums/showthread.php?t=590530
not sure how accurate the source is, but here Yochi Wada states FF13 should outsell FF7. if i can find more than one source with the same thing, it will be hard proof i think. of course, this was a long time ago, when they released it couldnt happen, they lowered it to 6 mil.
at the moment i accept this is not proof, its only one source, but still...