Teracopy's official page says "TeraCopy uses dynamically adjusted buffers to reduce the seek times.".
Wikipedia points to some tests:
In a test conducted in 2008 by lifehacker, Fastcopy was several times faster than it's rival Teracopy, a program with similar functionality. However, both programs have been updated since then. A more extensive comparison was performed between TeraCopy v2.07beta, KillCopy v2.85, FastCopy v1.99r4, SuperCopier v2.2bet and published on a forum in 2009.
I'm looking for more recent speed tests on Windows 7.