Why does doing a "Revision Graph" take so much longer than doing a "Show Log"?
The Revision Graph starts at the head and counts down to Revision 1. I'm up to over 1000 revisions and it takes about 1 minute to count down.
The Show Log is almost instant and only shows the revisions that this project has. There are only about 10 revisions for this project.
I believe the revision graph is not a built-in operation in the svn server, whereas the log is a built-in feature. To build the revision graph, TortoiseSVN has to generate many different queries against the server.
The revision graph needs the information that a log on the repository root, from HEAD to r1 returns.
So: if you show the full log for the repository root you should get the same time.
See this FAQ entry for an overview on how the graph works.