Pale Rider, with respect, I disagrree. Take a look at the specified weight for the Mk 2- 65 tons. Now mentally place a Mk4 next to it. The idea that such an increase in size, along with an increase in protection, larger main armament and larger engine could be gained for a ton or two is absurd. The Mk 2 with additional armor weighs more than 68 tons, so I dont thing that 75 tons or even 80 for the Mk 4 is impossible.