And I got thinking that to get the tank to go faster would require more than just an XL engine delivering more power. The Mars is a big 'ol tank and the closest thing we've ever really had to its quad track layout is the experimental T-95 tank destroyer which had two tracks on either side to support its not inconsiderable 95 tons.
The Mars has its tracks far more widely spread though and this would be a problem.
Those inner tracks would be a maintenance nightmare, if you throw one of the tracks or suffer damage to them, you can't have the crew work on them because the rest of the tank's in the way, everything track/roadwheel related would be a full on workshop job. And then there's the amount of space they take up internally, one of the inner tracks goes beneath the fighting compartment for the turret and although it seems to be an unmanned turret you've still probably got a turret basket and all the loading/power systems that would have to be placed around the area where the track bulges up into the hull. Unless the inner tracks are kind of like those on the TOG
Where they go up at the front and back for the drive wheels and then dip down to try and eliminate any major extension up into the hull.
But anyhow, the Mars XL. When making a vehicle, you have things like the clutch, the power system, breaks etc, all built to go to certain tolerances and speeds. If you then start doing things like adding weight etc you strain them and overwork them, leading to failures. We've had RL experience with this in WW2 where tanks like the Panther, Ferdinand/Elephant and Tiger II were too big and heavy for their transmissions or clutches and went through them at an alarming rate.
And slapping a more powerful engine into a Mars and expecting it to go faster would have the same problems. Its tracks, its suspension, clutch, transmission etc would all be built around a max speed of 32kph. Putting a more powerful engine in there and trying to force a system that is designed and built to do one thing by going well above what its meant to makes me think that the Mars XL would be an absolute nightmare for techs.
Even if you re-worked the Clutch, added a new gearbox and transmission as well as worked on the suspension and tracks, you'd probably have a vehicle that would have a voracious appetite for components. Something tells me that the Mars XL would be still rated to go at 32kph, and its driver and crew would be told that they could only 'give it the beans' to quote Clarkson for short periods of time and only basically in emergencies. Because if you don't you will break the power train or snap a track and you
will be stuck until techs or a dropship can get out to you (seeing as the Clans have nothing that i'm aware of that can recover and carry a Mars outside of a Dropship).