The problem is browser layout performance. I already described it in some detail in those earlier linked issues and pointed out some related Chrome bugs that have been filed, so I won't repeat all that here.
Collapsed events/groups don't do layout for their children - so if you tend to keep most things collapsed and only expand the content you're working on, it should be faster. Additionally spreading content across different event sheets will also help. In the longer term, most browser vendors (including Google) are currently in the process of completely rewriting their layout engines to be faster, more powerful and more flexible. I think this will do a lot to help once they start shipping the various parts of that. Keep an eye on LayoutNG for updates on Chrome's side.