A good starting point is mccrusher : https://github.com/memcached/mc-crusher
. "make" vs "make tls" will give you the corresponding client (mc-crusher vs mc-crusher-tls). Running mc-crusher and related tools to benchmark latency and throughput is explained in the README file.
Note that you can run memcached with and without TLS at the same time. e.g "./memcached -l notls:*:11211,*:22122". So you don't have to stop/start memcached for different tests. Also note that you need to run like this when capturing TLS numbers as tools provided with mc-crusher such as latency-sampler need a non-TLS socket to connect.
Keep in in mind that this is very basic test suit.