Imperial Guard tanks (mostly the Leman Russ and the Chimera) are vaguely similar in appearance to a combination of the British-produced Vickers A1E1 "Independent" and the Mark VIII "Liberty", although the A1E1 is fairly swift (32kph) and the Mark VIII is slow as sin (8.5 Kph). The A1E1 was rated as having an operational range of (approx.) 153 km, and the Mark VIII was about 81 km. A Leman Russ is listed as having a Cruising Speed of 35 kph; perhaps the M15-M25 (Dark Age of Technology) STC designs for its power plant, transmission, and suspension are superior to those of M2 (between WWI and WWII). That, or it has two inferior power plants…
Using the A1E1 as the base (one power plant, perhpas a V12 or larger), the Leman Russ MBT is (not quite) 1% faster, so it probably has an operational range of (approx.) 155 km, before requiring a refuel. Without getting into too many "technical" obscurities (like the fact that a MBT weighs 40% more than a Mark VIII), the power plant(s) of the MBT probably produce (approx.) 350-375 hp (maybe less if Prometheum is a WWI/WWII diesel equivalent; I don't remember reading anywhere that Prometheum "gels" in freezing temps like diesel, so there is that…).
I'm just throwing a number out (based very loosely on the M4 Sherman): the fuel capacity of a MBT is (approx.) 700 liters, which means it probably uses 4.5 liters per km. 700 liters is (approx.) 3.5 drums of fuel. As most MBT models have one, perhaps two drums banded to the rear skirting, you're looking at a fuel reserve of 210-420 liters, or an additional operating range of (approx.) 50-100 km.
Based on the MBT model (so scale is questionable) I'd say its main gun is at least 200mm (8"), if not more.
Ah, this page http://wh40k.lexican...nk#.UUhwu9YpxzM confirms that (as well as listing additional specs of the Leman Russ MBT). For those asking in other threads, the Clip of a Battle Cannon is 12, but the MBT carries an additional 28 shells in its shot locker and/or in the exterior boxes (or so says the link).
This was actually quite fun, as well as being useful to me for future referrence. I simply Googled "tanks, WWI" and looked for something resembling that big bastard from Indiana Jones: Raiders of the Lost Ark (which is actually a Mark VII; see here: http://indianajones....k?file=Tank.jpg).
Other tanks referrenced:
FCM Char C2 Heavy Tank/Super Heavy Tank (1921) http://www.militaryf...sp?armor_id=282 and http://www.chars-fra...0 poitou 01.jpg