Hi Johannes,It is indeed possible to use LDAP group permissions with SVN when using it with Apache (which is how I've always run it). http://gentoo-wiki.com/HOWTO_Apache2_with_subversion_SVN_and_DAV http://blogs.open.collab.net/svn/2007/03/subversion_ldap.html
I'd be happy to help with that.
Running SVN would give us access to the wonderful SVN::Notify, which I've attached a screenshot of.
And just as a reassurance for the IEM option, I've found SVN to be pretty light on resource use. There are only a few developers committing on any single day here.
Cheers Luke