I am thinking about switching to Git.
That would be a wise move. ;-)
I was able to install TortoiseGit and it works fine.
I recommend you rather learn the command line, and use the GUI tools that come standard with Git (eg: git-gui, gitk). They are ALWAYS the most up-to-date tools. Plus when using the command line, it is consistent across any platforms, and you have the full power of Git at your fingertips. I switched to Git in 2009, and on occation try out various Git GUI's and none of them can do everything you can do from the command line. They are all slower, cumbersome and take up desktop space (compared to a small terminal window).
So on SourceForge there would only be releases, and on GitHub there would be all changes.
I would ditch SourceForge completely. I'm actually thinking about doing the same thing with my projects. SourceForge supports Git (which is what I already use), but most of my projects are mirrored on Github too. Seeing that I frequently push and pull from both SourceForge and Github, I have immediately noticed that Github is so much faster. Plus, Github also supports project web pages, personal/author web pages, project binary releases, bug tracking, code review with inline comments etc.
Moving from SVN to Git is very easy too. Git can import the whole SVN history without trouble. Then simply add Github (or any other remote server) as a remote repository and push to that remote. Conversion - done!