xl1200 trivia (continued, sorry)

[pc@ctt.ctt.bellcore.com (Peter Clitherow)]

I've been using my XL1200 for a while now, and i'm very pleased with it.  i 
did notice one thing:  copying worlds between XL1200s starts off being many 
times faster than my old 3640, however, after 10k blocks or so of the world, 
performance degrades until after about 30k blocks it's no faster than
the G machines.  Is this an infelicity of the FAST-BLAST protocol,
problems allocating disk blocks fast enough or what?  The worlds being
copied are about 50k blocks btw, and both the sending and receiving
machines are XL1200s.

Ideas?

thanks
pc