Check out HPN-SSH, I use it extensively to transfer files over ssh, it provides a null cipher which you can use to disable encryption of data, while still maintaining encryption of authentication credentials.
http://www.psc.edu/networking/projects/hpn-ssh/
I transfer over a terrabyte of data a day using rsync+hpnssh.
Nate, That looks impressive, I would love to use that for other needs as well. How exactly do you go about installing this under CentOS? I can pretty well assume that patching the stock rpm would not work:)
Thanks! jlc