I am sorry if this has been brought up before, but I didn't remember seeing it.
On this page here you see a picture of a Mk.V**, and below the image is a link to a 23MB video of a Mk.V** on trials. It's a VERY cool video. This vehicle was a beast! In the background you can also see a Medium Mk.B I believe.
Edit: At first I thought that this footage must be very sped up. When the Mk.V** drives on flat terrain, it's really going fast! At the very least, it appears to be going over 4.6mph, the listed top speed for this vehicle. But, if you look at the motions of the people in the video, they don't seem that sped up, maybe just a little bit. Could this Mk.V** have been re-engined with a much more powerful engine?