I recall that all TCP versions after Vegas or Reno use pipelining to increase transfer speed. They send more than one segment before waiting for the ACK, and this of course multiplies the transfer rate by the number of segments. However, some TCP implementations either never initiate pipelining (it was the case of Windows XP) or use a low limit of 8 to the number of maximum outstanding (non-ACKed) segments, which does not push TCP to its potential.

See details here: http://gaia.cs.umass.edu/kurose/transport/congestion.html