Some complex subversion merges are coming up in my project: big branches that have been apart for a long time. Svn gives too many conflicts - and some of them seem spurious.
I've just worked through this myself. A simpler method is to pass git merge the --squash option, which will perform the merge without recording a merge commit, keeping the history linear so as not to confuse git-svn.
My merge was also very large, and I had to set git config diff.renamelimit 0 so that git would correctly find all the renames.