You do not need to synchronize the entire repository. You can clone the modules you need:
git svn clone --stdlayout http://myrepo/module
This will lead to the loss of the entire history for this module. You can just grab HEAD:
git svn clone --stdlayout -r HEAD http://myrepo/module
This is how I work most days.
many related questions about the workflow git-svn... just follow the links to the right of this answer :-)
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