Natural Breaks - Jenks

I have implemented Jenks' algorithm (for finding the natural breaks) in 
php thanks to some sample code I found at: 
http://www.mail-archive.com/r-sig-geo at stat.math.ethz.ch/msg00290.html . 
This algorithm is also implemented in ArcView to determine natural 
breaks in the legends.
Currently I am running the algorithm on a data set which has 65 000 
elements in it, which takes over 3 hours (due to a nested for loop). 
ArcViews' implementation on the other hand returns within seconds. Would 
anyone possibly know why ArcViews implementation is so much more efficient.

Any help would be greatly appreciated.

Ben Brehmer