I don't want to rant here, because it's a great picture, but my Warhammer fanboyism will never be satisfied otherwise.
This can't be a servitor. Servitors are specifically mind-wiped humans that have their minds re-programmed and their bodies outfitted with helpful cybernetics. There probably aren't any human components in this machine other than possibly the brain (because having limb structures and flesh inside those limbs would only get in the way).
So a war servitor would just be an armored gun/combat servitor, to better fulfill more combat roles and increase survivability, but its base would still be a human body, and its cybernetics scaled appropriately.
This would have to be an assault automata. And a fantastic one, I might add.
Right, then that would make it a Skitarii assault soldier or a heavy thallax unit if there was some scraps of humanity left inside. My first guess was be automata, because it looks like a machine built from the ground up, not around a human body. In that case, it would have a cyber-organic central computer.
I'm just saying that "servitor" is inappropriate. No Magos would take a servitor brain and put it inside a war machine as powerful as this, because they're usually badly damaged and hard-wired from the process of becoming a servitor, which is why servitors are constructed with specific jobs in mind that only require simple tasks. If they were going to implant someone's brain into the machine, they would not want to mind-wipe it first, and thus it would not be a servitor.