вы можете настроить vim так, чтобы он вел себя лучше с большими файлами:
http://www.vim.org/scripts/script.php?script_id=1506
Editing large files can be a time consuming process as Vim is working on a number of things behind the scenes, such as maintaining an undo database, searching for a syntax highlighting synchronization point, etc. LargeFile.vim is a very small "plugin"; mostly, its just an autocmd that disables certain features of vim in the interests of speed.