What perhaps would also help a lot would be using modern asynchronous / lazy page loading web technologies. Not sure if mediawiki is capable of this (without anyone patching it or its skin). Or perhaps there are other ways. Such as the approach by modpagespeed seems interesting. However, designing a professional high speed web site seems quite time consuming / skill demanding.
Varnish or not, page load speed or not, perhaps Main_Page is currently too heavy anyhow. Maybe too much content. Maybe too many screenshots.