I'm a big fan of tmux* and vim but there's a limit to the complexity of system that you can develop efficiently with vim. A good graphical IDE used by a skilled operator will be more likely to generate correct, consistent code faster. If you're using vim and think you're developing as well and as fast as you can, you're probably wrong. * 17 years of screen and I've finally switched over to tmux. None of the features…
I might look into tmux, screen is kind of buggy under cygwin.
There are plenty of code-completion plugins, and I used to have tab-completion enabled, but I never got around to adding it on my latest environment and don't miss it.
Of course, cscope is mostly useful for c/c++/java, but I've used the ruby vim map just fine. I operate on a codebase that's probably past a million lines of code. Maybe not all useful lines, I haven't seen them all ;)