I've used the standard Wordpress installation, with no extra plugins installed, not even Total Cache or Super Cache. I think that if you have Varnish Cache running on the server, there is no need for another Cache. Varnish uses RAM so it is more efficient than any Wordpress plugin. RAM is small in this server, if you need more space you can configure Varnish to also use disk as cache and then you have less used files on disk, and most accessed files on RAM.
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