VIM was very laggy for me after when I dialed my key repeat up. I know you're not supposed to but I sometimes just want to hold down j and scroll
When I would do this it would keep scrolling another 3-5 seconds after I let off the key.
Did some research and leared two very useful profileing tools built into VIM
:profile start profile.log :profile func * :profile file * " At this point do slow actions :profile pause :noautocmd qall!
This will let you track down plugins that are causing performance problems
And sometimes your problem is syntax highlighting (mine was)
:syntime on :syntime report