I've been unable to find the date of this paper, but the most recent cited paper in the references section is from 1999. I guess the paper itself is not much more recent than that. It contains a reference to a Cray computer with 512 CPUs at about 400 MHz.
I'm one of the authors. We wrote it in the summer of 1999 during the Pennsylvania Governor's School for the Sciences at Carnegie Mellon.
Getting access to a Cray T3E supercomputer as a high schooler was a beautiful thing. :)