About Caching. Redis,apcu,varnish,pagespeed

some can give me advices ? my cs-cart software running now APCU an redis.

i also installed mod_pagespeed with nginx . performance looking good.

anyway i thinking configure server with pagespeed downstream varnish.

what your thinks?

Cs-cart default caching systems (redis,apcu) will enough for performance ?

or muste be improve with mod pagespeed or varnish ? or pagespeed downstream with varnish ?