Well... I just went from mysql 5.6 to mariadb 10.1, and just wow... amazing how much that small amount of performance makes with a couple hundred people active online at once (not cookie session, actual live - huge gain).
For those who are graphical people... here is a 12hr snapshot of 5.6 - dip where I upgraded taking backup of server first - mariadb 10.1. Basically, my load issues where coming from the DB waiting on requests, and with six cores, I was getting annoyed at the waiting that was bottling up. As you can see to the right, my users were all there when I went live again, except this time with mariadb. Amazing difference. 5.6 was just horrible... especially when 5.5 looked more like the load after changing to mariadb. I expect upgrades to be better, not worse, for something like SQL DB's.
I normally hum along at a 2.5 - 3 load average when running mysql 5.5. It was getting ridiculous running 5.6. Mariadb is very nice once again.
My advice, stay on 5.5 or change to mariadb, but stay clear of mysql 5.6. Just horrible. And this is all with SSD cloud... 5.6 should be binned and never allowed on a production server.