Articles with large tables, especially articles that have plural large tables, are absolutely sluggish in VisualEditor. As in, on a PC powerful enough for folding@home and the like, I can count the seconds between each character showing up.
The particular article I can replicate this on is over here on the English wikipedia, but I've seen similar things on other articles too. The thing is, I don't even use the visual editing component of VisualEditor - I use the source editor - but that's made sluggish too.
I can theorise that some part of the visual editing parsing component is trying to run anyway, even with only source editing enabled - I don't know if this is actually what's happening, but it'd be great if it could not! Alternatively, perhaps one solution is disabling the live parse for articles with lots of wikitext and complex markup?