I have compared both versions. I think you can probably strip a lot of stuff from GS 3.4, for your specific needs. Removing Fontawesome folder from admin/template saves 1.8 mb, removing ckeditor skins except GetSimple saves you 0.8 mb and so on. You would have to strip this with every release, but you can make a script for that. I think this is a better solution than staying with old GS (well apart from possibly having better plugin support).
Also some files are double, minified and not minified, which makes sense for a source download. In the final version, the non minified files would get removed I think.
Also some files are double, minified and not minified, which makes sense for a source download. In the final version, the non minified files would get removed I think.