Hello Carl,
most of communications use TCP sessions.
TCP requires that the sender receives acks from receiver before moving on and sending other data.
So delay influences the capability to transfer data.
see
http://www.psc.edu/networking/projects/tcptune/
to overcome problems with high delay high speed links the extended TCP window has been introduced
see
http://www.ietf.org/rfc/rfc1323.txt
Hope to help
Giuseppe