Memcached considerably slows site…

Usually, that happens when your requests are too intensive for the memcached memory pool on shared environment. Unfortunatelly, we can’t doo much about this unless you upgrade to a cloud solution where we can have custom slab sizes for the service, etc. I would advise that if it has negative effect on your performance – just keep it off and use the rest of the optimizations. That’s why we don’t have it enabled by default – it really, really depends on the site itself and how it’s structured.