Disable / Configure Virus Scanner
One way of
speeding up subversion is to stop your virus checker from checking your working copy folders. (AVG is a big culprit of this).
AVG's Resident Shield scans every file that is added or update on your system, so it does this for every file retrieved in an update or checkout (which can be a lot) which slows down updates and checkouts considerably. Add an exception to ignore your working copy folders and Subversion will magically speed up.
Protocols
I did a benchmarking test to see whether the svn:// protocol was faster than the http(s):// and the results were almost identical. I could NOT find a difference in speed between them.