[CentOS] How to speed up Rsync transfers

Is there a way to speed up rsync transfers?
I tested the bandwidth with iperf (recommended to me in an earlier post &
worked well)its as advertised by my ISP's around 740KB/sec.
When I manually run my rsync script with the --progress switch the transfers
are around 100KB/sec.
I googled this and the only thing I found had to do with the TCP window
which I understand to be the limiting factor. But if this is true how can I
ftp stuff at 300KB/sec? (someone please enlighten me)

I'm backing up jpg files and some days they add 5+GB of images.
My goal was to backup the images nightly, but at the 100KB/sec rate that's
not possible.
Dan